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 $32.28   13.475%   $36.6297   $36.63   $36.65   $36.60  
  Purchase #2 $233.29   12.254%   $261.8774   $261.88   $261.90   $261.90  
  Purchase #3 $215.71   4.303%   $224.992   $224.99   $225.00   $225.00  
  Purchase #4 $236.98   7.653%   $255.1161   $255.12   $255.10   $255.10  
  Purchase #5 $85.50   6.327%   $90.9096   $90.91   $90.90   $90.90  
  Purchase #6 $119.78   4.679%   $125.3845   $125.38   $125.40   $125.40  
  Purchase #7 $234.34   3.543%   $242.6427   $242.64   $242.65   $242.60  
  7 purchase totals = $1,157.88       $1,237.5520   $1,237.55   $1,237.60   $1,237.50