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 $161.43   4.215%   $168.2343   $168.23   $168.25   $168.20  
  Purchase #2 $132.25   11.727%   $147.759   $147.76   $147.75   $147.80  
  Purchase #3 $81.78   8.443%   $88.6847   $88.68   $88.70   $88.70  
  Purchase #4 $153.68   7.447%   $165.1245   $165.12   $165.10   $165.10  
  Purchase #5 $248.96   13.594%   $282.8036   $282.80   $282.80   $282.80  
  Purchase #6 $179.25   12.105%   $200.9482   $200.95   $200.95   $200.90  
  Purchase #7 $245.47   12.575%   $276.3379   $276.34   $276.35   $276.30  
  7 purchase totals = $1,202.82       $1,329.8922   $1,329.88   $1,329.90   $1,329.80