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 $54.94   5.517%   $57.971   $57.97   $57.95   $58.00  
  Purchase #2 $137.98   11.777%   $154.2299   $154.23   $154.25   $154.20  
  Purchase #3 $14.29   12.779%   $16.1161   $16.12   $16.10   $16.10  
  Purchase #4 $177.28   8.187%   $191.7939   $191.79   $191.80   $191.80  
  Purchase #5 $92.46   12.594%   $104.1044   $104.10   $104.10   $104.10  
  Purchase #6 $66.49   13.185%   $75.2567   $75.26   $75.25   $75.30  
  Purchase #7 $157.95   6.774%   $168.6495   $168.65   $168.65   $168.60  
  7 purchase totals = $701.39       $768.1215   $768.12   $768.10   $768.10