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 $152.93   10.126%   $168.4157   $168.42   $168.40   $168.40  
  Purchase #2 $101.77   12.212%   $114.1982   $114.20   $114.20   $114.20  
  Purchase #3 $11.48   3.852%   $11.9222   $11.92   $11.90   $11.90  
  Purchase #4 $72.83   4.864%   $76.3725   $76.37   $76.35   $76.40  
  Purchase #5 $205.84   3.422%   $212.8838   $212.88   $212.90   $212.90  
  Purchase #6 $244.29   4.285%   $254.7578   $254.76   $254.75   $254.80  
  Purchase #7 $70.54   4.375%   $73.6261   $73.63   $73.65   $73.60  
  7 purchase totals = $859.68       $912.1763   $912.18   $912.15   $912.20