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 $58.41   11.516%   $65.1365   $65.14   $65.15   $65.10  
  Purchase #2 $76.26   3.682%   $79.0679   $79.07   $79.05   $79.10  
  Purchase #3 $10.93   11.119%   $12.1453   $12.15   $12.15   $12.10  
  Purchase #4 $244.78   9.327%   $267.6106   $267.61   $267.60   $267.60  
  Purchase #5 $76.36   9.388%   $83.5287   $83.53   $83.55   $83.50  
  Purchase #6 $199.35   5.756%   $210.8246   $210.82   $210.80   $210.80  
  Purchase #7 $65.38   6.828%   $69.8441   $69.84   $69.85   $69.80  
  7 purchase totals = $731.47       $788.1577   $788.16   $788.15   $788.00