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 $182.47   6.301%   $193.9674   $193.97   $193.95   $194.00  
  Purchase #2 $15.47   3.266%   $15.9753   $15.98   $16.00   $16.00  
  Purchase #3 $214.96   3.174%   $221.7828   $221.78   $221.80   $221.80  
  Purchase #4 $168.57   11.662%   $188.2286   $188.23   $188.25   $188.20  
  Purchase #5 $14.58   4.815%   $15.282   $15.28   $15.30   $15.30  
  Purchase #6 $98.62   9.311%   $107.8025   $107.80   $107.80   $107.80  
  Purchase #7 $89.30   13.869%   $101.685   $101.69   $101.70   $101.70  
  7 purchase totals = $783.97       $844.7236   $844.73   $844.80   $844.80