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 $146.34   12.469%   $164.5871   $164.59   $164.60   $164.60  
  Purchase #2 $93.39   5.138%   $98.1884   $98.19   $98.20   $98.20  
  Purchase #3 $206.93   6.353%   $220.0763   $220.08   $220.10   $220.10  
  Purchase #4 $96.33   11.601%   $107.5052   $107.51   $107.50   $107.50  
  Purchase #5 $75.30   10.297%   $83.0536   $83.05   $83.05   $83.10  
  Purchase #6 $86.38   13.225%   $97.8038   $97.80   $97.80   $97.80  
  Purchase #7 $160.33   12.571%   $180.4851   $180.49   $180.50   $180.50  
  7 purchase totals = $865.00       $951.6995   $951.71   $951.75   $951.80