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 $172.73   11.763%   $193.0482   $193.05   $193.05   $193.00  
  Purchase #2 $56.91   3.221%   $58.7431   $58.74   $58.75   $58.70  
  Purchase #3 $112.89   5.429%   $119.0188   $119.02   $119.00   $119.00  
  Purchase #4 $247.60   3.159%   $255.4217   $255.42   $255.40   $255.40  
  Purchase #5 $116.63   13.790%   $132.7133   $132.71   $132.70   $132.70  
  Purchase #6 $51.48   3.723%   $53.3966   $53.40   $53.40   $53.40  
  Purchase #7 $142.87   5.115%   $150.1778   $150.18   $150.20   $150.20  
  7 purchase totals = $901.11       $962.5195   $962.52   $962.50   $962.40