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 $212.47   7.132%   $227.6234   $227.62   $227.60   $227.60  
  Purchase #2 $113.43   4.517%   $118.5536   $118.55   $118.55   $118.60  
  Purchase #3 $18.75   3.796%   $19.4618   $19.46   $19.45   $19.50  
  Purchase #4 $184.93   12.637%   $208.2996   $208.30   $208.30   $208.30  
  Purchase #5 $8.50   9.638%   $9.3192   $9.32   $9.30   $9.30  
  Purchase #6 $68.40   6.716%   $72.9937   $72.99   $73.00   $73.00  
  Purchase #7 $104.61   8.533%   $113.5364   $113.54   $113.55   $113.50  
  7 purchase totals = $711.09       $769.7877   $769.78   $769.75   $769.80