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 $94.89   3.503%   $98.214   $98.21   $98.20   $98.20  
  Purchase #2 $191.57   13.353%   $217.1503   $217.15   $217.15   $217.20  
  Purchase #3 $113.99   5.607%   $120.3814   $120.38   $120.40   $120.40  
  Purchase #4 $188.92   5.489%   $199.2898   $199.29   $199.30   $199.30  
  Purchase #5 $30.91   13.305%   $35.0226   $35.02   $35.00   $35.00  
  Purchase #6 $109.43   4.871%   $114.7603   $114.76   $114.75   $114.80  
  Purchase #7 $204.54   5.417%   $215.6199   $215.62   $215.60   $215.60  
  7 purchase totals = $934.25       $1,000.4383   $1,000.43   $1,000.40   $1,000.50