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 $208.28   11.681%   $232.6092   $232.61   $232.60   $232.60  
  Purchase #2 $158.39   5.810%   $167.5925   $167.59   $167.60   $167.60  
  Purchase #3 $233.53   12.130%   $261.8572   $261.86   $261.85   $261.90  
  Purchase #4 $130.74   13.297%   $148.1245   $148.12   $148.10   $148.10  
  Purchase #5 $244.44   7.558%   $262.9148   $262.91   $262.90   $262.90  
  Purchase #6 $71.56   7.201%   $76.713   $76.71   $76.70   $76.70  
  Purchase #7 $210.26   12.404%   $236.3407   $236.34   $236.35   $236.30  
  7 purchase totals = $1,257.20       $1,386.1519   $1,386.14   $1,386.10   $1,386.10