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 $59.36   12.836%   $66.9794   $66.98   $67.00   $67.00  
  Purchase #2 $209.97   8.475%   $227.765   $227.77   $227.75   $227.80  
  Purchase #3 $90.25   4.580%   $94.3835   $94.38   $94.40   $94.40  
  Purchase #4 $93.28   8.390%   $101.1062   $101.11   $101.10   $101.10  
  Purchase #5 $208.43   6.519%   $222.0176   $222.02   $222.00   $222.00  
  Purchase #6 $154.90   9.655%   $169.8556   $169.86   $169.85   $169.90  
  Purchase #7 $110.88   5.322%   $116.781   $116.78   $116.80   $116.80  
  7 purchase totals = $927.07       $998.8883   $998.90   $998.90   $999.00