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 $203.98   11.622%   $227.6866   $227.69   $227.70   $227.70  
  Purchase #2 $68.47   11.828%   $76.5686   $76.57   $76.55   $76.60  
  Purchase #3 $93.63   8.491%   $101.5801   $101.58   $101.60   $101.60  
  Purchase #4 $54.31   8.863%   $59.1235   $59.12   $59.10   $59.10  
  Purchase #5 $15.78   6.698%   $16.8369   $16.84   $16.85   $16.80  
  Purchase #6 $87.36   3.354%   $90.2901   $90.29   $90.30   $90.30  
  Purchase #7 $174.33   9.547%   $190.9733   $190.97   $190.95   $191.00  
  7 purchase totals = $697.86       $763.0591   $763.06   $763.05   $763.10