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 $32.95   6.197%   $34.9919   $34.99   $35.00   $35.00  
  Purchase #2 $36.97   5.344%   $38.9457   $38.95   $38.95   $38.90  
  Purchase #3 $190.38   3.309%   $196.6797   $196.68   $196.70   $196.70  
  Purchase #4 $163.45   8.821%   $177.8679   $177.87   $177.85   $177.90  
  Purchase #5 $46.42   11.738%   $51.8688   $51.87   $51.85   $51.90  
  Purchase #6 $188.25   3.190%   $194.2552   $194.26   $194.25   $194.30  
  Purchase #7 $236.42   9.278%   $258.355   $258.36   $258.35   $258.40  
  7 purchase totals = $894.84       $952.9642   $952.98   $952.95   $953.10