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 $14.47   4.518%   $15.1238   $15.12   $15.10   $15.10  
  Purchase #2 $176.74   11.669%   $197.3638   $197.36   $197.35   $197.40  
  Purchase #3 $226.89   5.298%   $238.9106   $238.91   $238.90   $238.90  
  Purchase #4 $98.96   3.837%   $102.7571   $102.76   $102.75   $102.80  
  Purchase #5 $100.87   11.453%   $112.4226   $112.42   $112.40   $112.40  
  Purchase #6 $188.73   3.638%   $195.596   $195.60   $195.60   $195.60  
  Purchase #7 $60.94   4.395%   $63.6183   $63.62   $63.60   $63.60  
  7 purchase totals = $867.60       $925.7922   $925.79   $925.70   $925.80