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 $223.35   8.301%   $241.8903   $241.89   $241.90   $241.90  
  Purchase #2 $131.58   12.215%   $147.6525   $147.65   $147.65   $147.70  
  Purchase #3 $46.46   6.194%   $49.3377   $49.34   $49.35   $49.30  
  Purchase #4 $109.54   6.239%   $116.3742   $116.37   $116.35   $116.40  
  Purchase #5 $175.72   13.772%   $199.9202   $199.92   $199.90   $199.90  
  Purchase #6 $206.27   4.680%   $215.9234   $215.92   $215.90   $215.90  
  Purchase #7 $172.78   7.678%   $186.046   $186.05   $186.05   $186.00  
  7 purchase totals = $1,065.70       $1,157.1443   $1,157.14   $1,157.10   $1,157.10