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 $211.42   13.779%   $240.5516   $240.55   $240.55   $240.60  
  Purchase #2 $232.47   10.198%   $256.1773   $256.18   $256.20   $256.20  
  Purchase #3 $247.47   6.392%   $263.2883   $263.29   $263.30   $263.30  
  Purchase #4 $72.29   5.526%   $76.2847   $76.28   $76.30   $76.30  
  Purchase #5 $186.77   6.165%   $198.2844   $198.28   $198.30   $198.30  
  Purchase #6 $229.93   8.159%   $248.69   $248.69   $248.70   $248.70  
  Purchase #7 $180.47   4.778%   $189.0929   $189.09   $189.10   $189.10  
  7 purchase totals = $1,360.82       $1,472.3692   $1,472.36   $1,472.45   $1,472.50