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 $146.35   10.469%   $161.6714   $161.67   $161.65   $161.70  
  Purchase #2 $227.39   10.374%   $250.9794   $250.98   $251.00   $251.00  
  Purchase #3 $21.38   9.229%   $23.3532   $23.35   $23.35   $23.40  
  Purchase #4 $172.49   13.451%   $195.6916   $195.69   $195.70   $195.70  
  Purchase #5 $70.76   3.656%   $73.347   $73.35   $73.35   $73.30  
  Purchase #6 $10.62   7.327%   $11.3981   $11.40   $11.40   $11.40  
  Purchase #7 $42.75   10.726%   $47.3354   $47.34   $47.35   $47.30  
  7 purchase totals = $691.74       $763.7761   $763.78   $763.80   $763.80