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 $63.73   6.616%   $67.9464   $67.95   $67.95   $67.90  
  Purchase #2 $214.31   10.382%   $236.5597   $236.56   $236.55   $236.60  
  Purchase #3 $41.73   13.595%   $47.4032   $47.40   $47.40   $47.40  
  Purchase #4 $189.26   10.570%   $209.2648   $209.26   $209.25   $209.30  
  Purchase #5 $217.80   11.379%   $242.5835   $242.58   $242.60   $242.60  
  Purchase #6 $20.49   6.396%   $21.8005   $21.80   $21.80   $21.80  
  Purchase #7 $124.99   5.837%   $132.2857   $132.29   $132.30   $132.30  
  7 purchase totals = $872.31       $957.8438   $957.84   $957.85   $957.90