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 $54.74   7.329%   $58.7519   $58.75   $58.75   $58.80  
  Purchase #2 $87.39   11.539%   $97.4739   $97.47   $97.45   $97.50  
  Purchase #3 $244.77   6.378%   $260.3814   $260.38   $260.40   $260.40  
  Purchase #4 $38.52   5.742%   $40.7318   $40.73   $40.75   $40.70  
  Purchase #5 $153.91   10.412%   $169.9351   $169.94   $169.95   $169.90  
  Purchase #6 $220.48   10.395%   $243.3989   $243.40   $243.40   $243.40  
  Purchase #7 $59.83   12.568%   $67.3494   $67.35   $67.35   $67.30  
  7 purchase totals = $859.64       $938.0224   $938.02   $938.05   $938.00