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 $213.83   8.267%   $231.5073   $231.51   $231.50   $231.50  
  Purchase #2 $69.77   8.330%   $75.5818   $75.58   $75.60   $75.60  
  Purchase #3 $153.30   8.735%   $166.6908   $166.69   $166.70   $166.70  
  Purchase #4 $132.29   5.412%   $139.4495   $139.45   $139.45   $139.40  
  Purchase #5 $9.92   7.177%   $10.632   $10.63   $10.65   $10.60  
  Purchase #6 $76.39   3.632%   $79.1645   $79.16   $79.15   $79.20  
  Purchase #7 $199.94   13.676%   $227.2838   $227.28   $227.30   $227.30  
  7 purchase totals = $855.44       $930.3097   $930.30   $930.35   $930.30