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 $243.68   10.792%   $269.9779   $269.98   $270.00   $270.00  
  Purchase #2 $44.45   4.152%   $46.2956   $46.30   $46.30   $46.30  
  Purchase #3 $32.65   5.782%   $34.5378   $34.54   $34.55   $34.50  
  Purchase #4 $216.84   7.704%   $233.5454   $233.55   $233.55   $233.50  
  Purchase #5 $234.65   11.609%   $261.8905   $261.89   $261.90   $261.90  
  Purchase #6 $249.99   8.780%   $271.9391   $271.94   $271.95   $271.90  
  Purchase #7 $22.32   12.181%   $25.0388   $25.04   $25.05   $25.00  
  7 purchase totals = $1,044.58       $1,143.2251   $1,143.24   $1,143.30   $1,143.10