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 $183.74   6.169%   $195.0749   $195.07   $195.05   $195.10  
  Purchase #2 $46.80   8.819%   $50.9273   $50.93   $50.95   $50.90  
  Purchase #3 $35.45   4.352%   $36.9928   $36.99   $37.00   $37.00  
  Purchase #4 $212.57   5.539%   $224.3443   $224.34   $224.35   $224.30  
  Purchase #5 $68.73   13.519%   $78.0216   $78.02   $78.00   $78.00  
  Purchase #6 $221.32   10.481%   $244.5165   $244.52   $244.50   $244.50  
  Purchase #7 $217.62   8.455%   $236.0198   $236.02   $236.00   $236.00  
  7 purchase totals = $986.23       $1,065.8972   $1,065.89   $1,065.85   $1,065.80