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 $63.76   11.231%   $70.9209   $70.92   $70.90   $70.90  
  Purchase #2 $220.68   13.722%   $250.9617   $250.96   $250.95   $251.00  
  Purchase #3 $82.86   4.106%   $86.2622   $86.26   $86.25   $86.30  
  Purchase #4 $40.94   12.853%   $46.202   $46.20   $46.20   $46.20  
  Purchase #5 $132.89   3.505%   $137.5478   $137.55   $137.55   $137.50  
  Purchase #6 $159.32   4.290%   $166.1548   $166.15   $166.15   $166.20  
  Purchase #7 $94.65   7.481%   $101.7308   $101.73   $101.75   $101.70  
  7 purchase totals = $795.10       $859.7802   $859.77   $859.75   $859.80