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 $68.46   11.832%   $76.5602   $76.56   $76.55   $76.60  
  Purchase #2 $204.98   4.322%   $213.8392   $213.84   $213.85   $213.80  
  Purchase #3 $180.49   8.303%   $195.4761   $195.48   $195.50   $195.50  
  Purchase #4 $231.41   11.292%   $257.5408   $257.54   $257.55   $257.50  
  Purchase #5 $40.57   3.858%   $42.1352   $42.14   $42.15   $42.10  
  Purchase #6 $12.34   10.460%   $13.6308   $13.63   $13.65   $13.60  
  Purchase #7 $129.34   13.218%   $146.4362   $146.44   $146.45   $146.40  
  7 purchase totals = $867.59       $945.6185   $945.63   $945.70   $945.50