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 $81.97   4.586%   $85.7291   $85.73   $85.75   $85.70  
  Purchase #2 $81.79   11.638%   $91.3087   $91.31   $91.30   $91.30  
  Purchase #3 $229.50   13.181%   $259.7504   $259.75   $259.75   $259.80  
  Purchase #4 $98.63   4.713%   $103.2784   $103.28   $103.30   $103.30  
  Purchase #5 $8.95   3.859%   $9.2954   $9.30   $9.30   $9.30  
  Purchase #6 $152.89   5.871%   $161.8662   $161.87   $161.85   $161.90  
  Purchase #7 $210.39   5.388%   $221.7258   $221.73   $221.75   $221.70  
  7 purchase totals = $864.12       $932.9540   $932.97   $933.00   $933.00