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 $92.95   5.419%   $97.987   $97.99   $98.00   $98.00  
  Purchase #2 $242.56   9.182%   $264.8319   $264.83   $264.85   $264.80  
  Purchase #3 $90.58   6.181%   $96.1787   $96.18   $96.20   $96.20  
  Purchase #4 $162.92   4.670%   $170.5284   $170.53   $170.55   $170.50  
  Purchase #5 $83.70   3.105%   $86.2989   $86.30   $86.30   $86.30  
  Purchase #6 $165.39   6.375%   $175.9336   $175.93   $175.95   $175.90  
  Purchase #7 $98.39   3.513%   $101.8464   $101.85   $101.85   $101.80  
  7 purchase totals = $936.49       $993.6049   $993.61   $993.70   $993.50