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 $222.69   13.713%   $253.2275   $253.23   $253.25   $253.20  
  Purchase #2 $22.49   8.509%   $24.4037   $24.40   $24.40   $24.40  
  Purchase #3 $82.56   6.638%   $88.0403   $88.04   $88.05   $88.00  
  Purchase #4 $125.30   5.697%   $132.4383   $132.44   $132.45   $132.40  
  Purchase #5 $126.62   10.306%   $139.6695   $139.67   $139.65   $139.70  
  Purchase #6 $177.82   11.494%   $198.2586   $198.26   $198.25   $198.30  
  Purchase #7 $28.48   3.158%   $29.3794   $29.38   $29.40   $29.40  
  7 purchase totals = $785.96       $865.4173   $865.42   $865.45   $865.40