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 $219.64   7.772%   $236.7104   $236.71   $236.70   $236.70  
  Purchase #2 $215.93   13.251%   $244.5429   $244.54   $244.55   $244.50  
  Purchase #3 $48.47   11.321%   $53.9573   $53.96   $53.95   $54.00  
  Purchase #4 $59.49   4.564%   $62.2051   $62.21   $62.20   $62.20  
  Purchase #5 $126.25   10.554%   $139.5744   $139.57   $139.55   $139.60  
  Purchase #6 $115.55   3.451%   $119.5376   $119.54   $119.55   $119.50  
  Purchase #7 $66.93   4.730%   $70.0958   $70.10   $70.10   $70.10  
  7 purchase totals = $852.26       $926.6235   $926.63   $926.60   $926.60