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 $226.67   8.510%   $245.9596   $245.96   $245.95   $246.00  
  Purchase #2 $183.26   11.118%   $203.6348   $203.63   $203.65   $203.60  
  Purchase #3 $149.90   9.874%   $164.7011   $164.70   $164.70   $164.70  
  Purchase #4 $81.81   7.416%   $87.877   $87.88   $87.90   $87.90  
  Purchase #5 $163.71   13.848%   $186.3806   $186.38   $186.40   $186.40  
  Purchase #6 $25.96   13.304%   $29.4137   $29.41   $29.40   $29.40  
  Purchase #7 $217.93   7.103%   $233.4096   $233.41   $233.40   $233.40  
  7 purchase totals = $1,049.24       $1,151.3764   $1,151.37   $1,151.40   $1,151.40