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 $59.39   4.419%   $62.0144   $62.01   $62.00   $62.00  
  Purchase #2 $84.74   10.382%   $93.5377   $93.54   $93.55   $93.50  
  Purchase #3 $149.73   4.763%   $156.8616   $156.86   $156.85   $156.90  
  Purchase #4 $206.89   12.614%   $232.9871   $232.99   $233.00   $233.00  
  Purchase #5 $109.62   9.423%   $119.9495   $119.95   $119.95   $119.90  
  Purchase #6 $53.51   4.176%   $55.7446   $55.74   $55.75   $55.70  
  Purchase #7 $224.52   4.555%   $234.7469   $234.75   $234.75   $234.70  
  7 purchase totals = $888.40       $955.8418   $955.84   $955.85   $955.70