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 $60.75   11.839%   $67.9422   $67.94   $67.95   $67.90  
  Purchase #2 $218.87   11.183%   $243.3462   $243.35   $243.35   $243.30  
  Purchase #3 $240.45   12.733%   $271.0665   $271.07   $271.05   $271.10  
  Purchase #4 $93.54   8.635%   $101.6172   $101.62   $101.60   $101.60  
  Purchase #5 $35.75   3.208%   $36.8969   $36.90   $36.90   $36.90  
  Purchase #6 $198.72   8.197%   $215.0091   $215.01   $215.00   $215.00  
  Purchase #7 $25.74   5.841%   $27.2435   $27.24   $27.25   $27.20  
  7 purchase totals = $873.82       $963.1216   $963.13   $963.10   $963.00