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 $63.76   7.609%   $68.6115   $68.61   $68.60   $68.60  
  Purchase #2 $137.39   11.616%   $153.3492   $153.35   $153.35   $153.30  
  Purchase #3 $32.30   6.441%   $34.3804   $34.38   $34.40   $34.40  
  Purchase #4 $134.86   8.204%   $145.9239   $145.92   $145.90   $145.90  
  Purchase #5 $78.39   7.741%   $84.4582   $84.46   $84.45   $84.50  
  Purchase #6 $172.92   13.105%   $195.5812   $195.58   $195.60   $195.60  
  Purchase #7 $211.47   9.177%   $230.8766   $230.88   $230.90   $230.90  
  7 purchase totals = $831.09       $913.1810   $913.18   $913.20   $913.20