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 $245.41   7.152%   $262.9617   $262.96   $262.95   $263.00  
  Purchase #2 $115.95   8.578%   $125.8962   $125.90   $125.90   $125.90  
  Purchase #3 $167.92   8.751%   $182.6147   $182.61   $182.60   $182.60  
  Purchase #4 $105.75   5.384%   $111.4436   $111.44   $111.45   $111.40  
  Purchase #5 $87.88   5.220%   $92.4673   $92.47   $92.45   $92.50  
  Purchase #6 $143.99   9.461%   $157.6129   $157.61   $157.60   $157.60  
  Purchase #7 $77.92   13.509%   $88.4462   $88.45   $88.45   $88.40  
  7 purchase totals = $944.82       $1,021.4426   $1,021.44   $1,021.40   $1,021.40