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 $229.75   10.336%   $253.497   $253.50   $253.50   $253.50  
  Purchase #2 $59.43   4.246%   $61.9534   $61.95   $61.95   $62.00  
  Purchase #3 $144.26   12.785%   $162.7036   $162.70   $162.70   $162.70  
  Purchase #4 $92.57   11.202%   $102.9397   $102.94   $102.95   $102.90  
  Purchase #5 $65.56   8.366%   $71.0447   $71.04   $71.05   $71.00  
  Purchase #6 $59.98   13.624%   $68.1517   $68.15   $68.15   $68.20  
  Purchase #7 $95.60   5.652%   $101.0033   $101.00   $101.00   $101.00  
  7 purchase totals = $747.15       $821.2934   $821.28   $821.30   $821.30