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 $69.34   10.604%   $76.6928   $76.69   $76.70   $76.70  
  Purchase #2 $25.76   4.111%   $26.819   $26.82   $26.80   $26.80  
  Purchase #3 $96.78   12.382%   $108.7633   $108.76   $108.75   $108.80  
  Purchase #4 $237.92   9.355%   $260.1774   $260.18   $260.20   $260.20  
  Purchase #5 $170.89   5.383%   $180.089   $180.09   $180.10   $180.10  
  Purchase #6 $58.67   12.765%   $66.1592   $66.16   $66.15   $66.20  
  Purchase #7 $243.98   11.488%   $272.0084   $272.01   $272.00   $272.00  
  7 purchase totals = $903.34       $990.7091   $990.71   $990.70   $990.80