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 $250.72   4.489%   $261.9748   $261.97   $261.95   $262.00  
  Purchase #2 $51.69   4.462%   $53.9964   $54.00   $54.00   $54.00  
  Purchase #3 $101.64   3.576%   $105.2746   $105.27   $105.25   $105.30  
  Purchase #4 $51.70   11.276%   $57.5297   $57.53   $57.55   $57.50  
  Purchase #5 $206.76   8.854%   $225.0665   $225.07   $225.05   $225.10  
  Purchase #6 $64.39   11.518%   $71.8064   $71.81   $71.80   $71.80  
  Purchase #7 $199.68   12.323%   $224.2866   $224.29   $224.30   $224.30  
  7 purchase totals = $926.58       $999.9350   $999.94   $999.90   $1,000.00