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 $77.46   11.200%   $86.1355   $86.14   $86.15   $86.10  
  Purchase #2 $52.73   6.827%   $56.3299   $56.33   $56.35   $56.30  
  Purchase #3 $109.54   8.842%   $119.2255   $119.23   $119.25   $119.20  
  Purchase #4 $95.83   12.422%   $107.734   $107.73   $107.75   $107.70  
  Purchase #5 $131.62   7.599%   $141.6218   $141.62   $141.60   $141.60  
  Purchase #6 $182.95   8.729%   $198.9197   $198.92   $198.90   $198.90  
  Purchase #7 $91.55   3.610%   $94.855   $94.86   $94.85   $94.90  
  7 purchase totals = $741.68       $804.8214   $804.83   $804.85   $804.70