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 $19.42   3.407%   $20.0816   $20.08   $20.10   $20.10  
  Purchase #2 $30.78   4.430%   $32.1436   $32.14   $32.15   $32.10  
  Purchase #3 $149.73   10.344%   $165.2181   $165.22   $165.20   $165.20  
  Purchase #4 $138.87   5.648%   $146.7134   $146.71   $146.70   $146.70  
  Purchase #5 $103.88   6.644%   $110.7818   $110.78   $110.80   $110.80  
  Purchase #6 $217.70   8.377%   $235.9367   $235.94   $235.95   $235.90  
  Purchase #7 $48.44   3.513%   $50.1417   $50.14   $50.15   $50.10  
  7 purchase totals = $708.82       $761.0169   $761.01   $761.05   $760.90