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 $235.32   5.801%   $248.9709   $248.97   $248.95   $249.00  
  Purchase #2 $223.69   4.244%   $233.1834   $233.18   $233.20   $233.20  
  Purchase #3 $213.28   13.465%   $241.9982   $242.00   $242.00   $242.00  
  Purchase #4 $214.35   9.345%   $234.381   $234.38   $234.40   $234.40  
  Purchase #5 $95.90   9.346%   $104.8628   $104.86   $104.85   $104.90  
  Purchase #6 $57.28   5.316%   $60.325   $60.33   $60.35   $60.30  
  Purchase #7 $76.71   7.340%   $82.3405   $82.34   $82.35   $82.30  
  7 purchase totals = $1,116.53       $1,206.0618   $1,206.06   $1,206.10   $1,206.10