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 $59.43   11.517%   $66.2746   $66.27   $66.25   $66.30  
  Purchase #2 $211.46   9.632%   $231.8278   $231.83   $231.85   $231.80  
  Purchase #3 $20.60   6.667%   $21.9734   $21.97   $21.95   $22.00  
  Purchase #4 $167.73   8.819%   $182.5221   $182.52   $182.50   $182.50  
  Purchase #5 $96.63   3.357%   $99.8739   $99.87   $99.85   $99.90  
  Purchase #6 $115.31   3.852%   $119.7517   $119.75   $119.75   $119.80  
  Purchase #7 $237.73   6.425%   $253.0042   $253.00   $253.00   $253.00  
  7 purchase totals = $908.89       $975.2277   $975.21   $975.15   $975.30