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 $174.58   13.373%   $197.9266   $197.93   $197.95   $197.90  
  Purchase #2 $17.73   9.192%   $19.3597   $19.36   $19.35   $19.40  
  Purchase #3 $132.86   11.589%   $148.2571   $148.26   $148.25   $148.30  
  Purchase #4 $39.33   9.733%   $43.158   $43.16   $43.15   $43.20  
  Purchase #5 $51.78   10.810%   $57.3774   $57.38   $57.40   $57.40  
  Purchase #6 $95.89   8.546%   $104.0848   $104.08   $104.10   $104.10  
  Purchase #7 $51.83   5.240%   $54.5459   $54.55   $54.55   $54.50  
  7 purchase totals = $564.00       $624.7095   $624.72   $624.75   $624.80