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 $227.86   8.473%   $247.1666   $247.17   $247.15   $247.20  
  Purchase #2 $223.75   5.344%   $235.7072   $235.71   $235.70   $235.70  
  Purchase #3 $167.86   9.734%   $184.1995   $184.20   $184.20   $184.20  
  Purchase #4 $18.95   3.342%   $19.5833   $19.58   $19.60   $19.60  
  Purchase #5 $111.55   12.387%   $125.3677   $125.37   $125.35   $125.40  
  Purchase #6 $148.55   10.626%   $164.3349   $164.33   $164.35   $164.30  
  Purchase #7 $98.62   8.776%   $107.2749   $107.27   $107.25   $107.30  
  7 purchase totals = $997.14       $1,083.6341   $1,083.63   $1,083.60   $1,083.70