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 $55.98   4.828%   $58.6827   $58.68   $58.70   $58.70  
  Purchase #2 $242.95   4.413%   $253.6714   $253.67   $253.65   $253.70  
  Purchase #3 $22.79   10.486%   $25.1798   $25.18   $25.20   $25.20  
  Purchase #4 $200.51   11.807%   $224.1842   $224.18   $224.20   $224.20  
  Purchase #5 $176.87   6.517%   $188.3966   $188.40   $188.40   $188.40  
  Purchase #6 $142.89   7.763%   $153.9826   $153.98   $154.00   $154.00  
  Purchase #7 $53.52   3.571%   $55.4312   $55.43   $55.45   $55.40  
  7 purchase totals = $895.51       $959.5285   $959.52   $959.60   $959.60