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 $248.61   7.691%   $267.7306   $267.73   $267.75   $267.70  
  Purchase #2 $23.86   4.230%   $24.8693   $24.87   $24.85   $24.90  
  Purchase #3 $20.76   11.217%   $23.0886   $23.09   $23.10   $23.10  
  Purchase #4 $63.54   13.387%   $72.0461   $72.05   $72.05   $72.00  
  Purchase #5 $213.92   9.773%   $234.8264   $234.83   $234.85   $234.80  
  Purchase #6 $219.57   10.629%   $242.9081   $242.91   $242.90   $242.90  
  Purchase #7 $62.75   10.362%   $69.2522   $69.25   $69.25   $69.30  
  7 purchase totals = $853.01       $934.7213   $934.73   $934.75   $934.70