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 $67.27   13.279%   $76.2028   $76.20   $76.20   $76.20  
  Purchase #2 $133.94   3.351%   $138.4283   $138.43   $138.45   $138.40  
  Purchase #3 $108.48   10.577%   $119.9539   $119.95   $119.95   $120.00  
  Purchase #4 $170.38   6.871%   $182.0868   $182.09   $182.10   $182.10  
  Purchase #5 $37.71   7.111%   $40.3916   $40.39   $40.40   $40.40  
  Purchase #6 $128.74   8.441%   $139.6069   $139.61   $139.60   $139.60  
  Purchase #7 $34.43   3.196%   $35.5304   $35.53   $35.55   $35.50  
  7 purchase totals = $680.95       $732.2007   $732.20   $732.25   $732.20