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 $236.96   7.724%   $255.2628   $255.26   $255.25   $255.30  
  Purchase #2 $58.28   8.509%   $63.239   $63.24   $63.25   $63.20  
  Purchase #3 $236.31   9.125%   $257.8733   $257.87   $257.85   $257.90  
  Purchase #4 $199.79   10.412%   $220.5921   $220.59   $220.60   $220.60  
  Purchase #5 $72.95   4.627%   $76.3254   $76.33   $76.35   $76.30  
  Purchase #6 $5.86   3.577%   $6.0696   $6.07   $6.05   $6.10  
  Purchase #7 $131.59   3.441%   $136.118   $136.12   $136.10   $136.10  
  7 purchase totals = $941.74       $1,015.4802   $1,015.48   $1,015.45   $1,015.50