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 $191.69   13.152%   $216.9011   $216.90   $216.90   $216.90  
  Purchase #2 $48.69   5.692%   $51.4614   $51.46   $51.45   $51.50  
  Purchase #3 $180.72   8.414%   $195.9258   $195.93   $195.95   $195.90  
  Purchase #4 $83.47   10.526%   $92.2561   $92.26   $92.25   $92.30  
  Purchase #5 $156.44   7.249%   $167.7803   $167.78   $167.80   $167.80  
  Purchase #6 $104.31   11.138%   $115.928   $115.93   $115.95   $115.90  
  Purchase #7 $84.76   11.538%   $94.5396   $94.54   $94.55   $94.50  
  7 purchase totals = $850.08       $934.7923   $934.80   $934.85   $934.80