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 $104.63   12.327%   $117.5277   $117.53   $117.55   $117.50  
  Purchase #2 $43.84   7.611%   $47.1767   $47.18   $47.20   $47.20  
  Purchase #3 $57.53   10.699%   $63.6851   $63.69   $63.70   $63.70  
  Purchase #4 $61.36   4.508%   $64.1261   $64.13   $64.15   $64.10  
  Purchase #5 $111.66   12.291%   $125.3841   $125.38   $125.40   $125.40  
  Purchase #6 $182.26   13.474%   $206.8177   $206.82   $206.80   $206.80  
  Purchase #7 $184.64   9.126%   $201.4902   $201.49   $201.50   $201.50  
  7 purchase totals = $745.92       $826.2076   $826.22   $826.30   $826.20