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 $93.65   11.351%   $104.2802   $104.28   $104.30   $104.30  
  Purchase #2 $195.69   6.787%   $208.9715   $208.97   $208.95   $209.00  
  Purchase #3 $88.90   6.752%   $94.9025   $94.90   $94.90   $94.90  
  Purchase #4 $124.38   6.627%   $132.6227   $132.62   $132.60   $132.60  
  Purchase #5 $87.89   4.686%   $92.0085   $92.01   $92.00   $92.00  
  Purchase #6 $92.42   6.829%   $98.7314   $98.73   $98.75   $98.70  
  Purchase #7 $223.60   6.352%   $237.8031   $237.80   $237.80   $237.80  
  7 purchase totals = $906.53       $969.3199   $969.31   $969.30   $969.30