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 $94.53   6.802%   $100.9599   $100.96   $100.95   $101.00  
  Purchase #2 $236.78   11.354%   $263.664   $263.66   $263.65   $263.70  
  Purchase #3 $190.90   11.308%   $212.487   $212.49   $212.50   $212.50  
  Purchase #4 $18.95   12.353%   $21.2909   $21.29   $21.30   $21.30  
  Purchase #5 $98.57   6.392%   $104.8706   $104.87   $104.85   $104.90  
  Purchase #6 $166.43   9.557%   $182.3357   $182.34   $182.35   $182.30  
  Purchase #7 $46.95   9.790%   $51.5464   $51.55   $51.55   $51.50  
  7 purchase totals = $853.11       $937.1545   $937.16   $937.15   $937.20