Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.58   10.471%   $239.2581   $239.26   $239.25   $239.30  
  Purchase #2 $195.61   10.283%   $215.7246   $215.72   $215.70   $215.70  
  Purchase #3 $213.44   11.822%   $238.6729   $238.67   $238.65   $238.70  
  Purchase #4 $228.80   13.556%   $259.8161   $259.82   $259.80   $259.80  
  Purchase #5 $192.37   6.228%   $204.3508   $204.35   $204.35   $204.40  
  Purchase #6 $164.80   7.214%   $176.6887   $176.69   $176.70   $176.70  
  Purchase #7 $213.73   13.180%   $241.8996   $241.90   $241.90   $241.90  
  7 purchase totals = $1,425.33       $1,576.4108   $1,576.41   $1,576.35   $1,576.50