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 $96.60   5.432%   $101.8473   $101.85   $101.85   $101.80  
  Purchase #2 $100.89   3.443%   $104.3636   $104.36   $104.35   $104.40  
  Purchase #3 $90.73   13.699%   $103.1591   $103.16   $103.15   $103.20  
  Purchase #4 $81.95   7.511%   $88.1053   $88.11   $88.10   $88.10  
  Purchase #5 $112.66   4.664%   $117.9145   $117.91   $117.90   $117.90  
  Purchase #6 $217.91   12.328%   $244.7739   $244.77   $244.75   $244.80  
  Purchase #7 $24.59   7.801%   $26.5083   $26.51   $26.50   $26.50  
  7 purchase totals = $725.33       $786.6720   $786.67   $786.60   $786.70