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 $229.54   13.864%   $261.3634   $261.36   $261.35   $261.40  
  Purchase #2 $91.71   11.828%   $102.5575   $102.56   $102.55   $102.60  
  Purchase #3 $49.60   4.646%   $51.9044   $51.90   $51.90   $51.90  
  Purchase #4 $141.90   11.184%   $157.7701   $157.77   $157.75   $157.80  
  Purchase #5 $248.40   4.837%   $260.4151   $260.42   $260.40   $260.40  
  Purchase #6 $213.62   10.844%   $236.785   $236.79   $236.80   $236.80  
  Purchase #7 $165.50   10.695%   $183.2002   $183.20   $183.20   $183.20  
  7 purchase totals = $1,140.27       $1,253.9957   $1,254.00   $1,253.95   $1,254.10