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 $78.28   10.151%   $86.2262   $86.23   $86.25   $86.20  
  Purchase #2 $18.37   4.736%   $19.24   $19.24   $19.25   $19.20  
  Purchase #3 $26.87   3.313%   $27.7602   $27.76   $27.75   $27.80  
  Purchase #4 $245.58   6.505%   $261.555   $261.56   $261.55   $261.60  
  Purchase #5 $92.59   4.327%   $96.5964   $96.60   $96.60   $96.60  
  Purchase #6 $30.82   10.869%   $34.1698   $34.17   $34.15   $34.20  
  Purchase #7 $78.49   12.515%   $88.313   $88.31   $88.30   $88.30  
  7 purchase totals = $571.00       $613.8606   $613.87   $613.85   $613.90