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 $218.88   6.537%   $233.1882   $233.19   $233.20   $233.20  
  Purchase #2 $71.97   7.815%   $77.5945   $77.59   $77.60   $77.60  
  Purchase #3 $17.85   5.151%   $18.7695   $18.77   $18.75   $18.80  
  Purchase #4 $119.73   5.629%   $126.4696   $126.47   $126.45   $126.50  
  Purchase #5 $132.54   3.563%   $137.2624   $137.26   $137.25   $137.30  
  Purchase #6 $41.68   4.182%   $43.4231   $43.42   $43.40   $43.40  
  Purchase #7 $92.75   11.733%   $103.6324   $103.63   $103.65   $103.60  
  7 purchase totals = $695.40       $740.3397   $740.33   $740.30   $740.40