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 $41.61   11.373%   $46.3423   $46.34   $46.35   $46.30  
  Purchase #2 $171.44   13.214%   $194.0941   $194.09   $194.10   $194.10  
  Purchase #3 $221.95   12.781%   $250.3174   $250.32   $250.30   $250.30  
  Purchase #4 $90.25   6.348%   $95.9791   $95.98   $96.00   $96.00  
  Purchase #5 $95.26   5.376%   $100.3812   $100.38   $100.40   $100.40  
  Purchase #6 $161.97   9.763%   $177.7831   $177.78   $177.80   $177.80  
  Purchase #7 $12.47   4.513%   $13.0328   $13.03   $13.05   $13.00  
  7 purchase totals = $794.95       $877.9300   $877.92   $878.00   $877.90