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 $224.65   3.278%   $232.014   $232.01   $232.00   $232.00  
  Purchase #2 $185.59   3.827%   $192.6925   $192.69   $192.70   $192.70  
  Purchase #3 $158.96   7.571%   $170.9949   $170.99   $171.00   $171.00  
  Purchase #4 $233.43   3.769%   $242.228   $242.23   $242.25   $242.20  
  Purchase #5 $227.42   5.172%   $239.1822   $239.18   $239.20   $239.20  
  Purchase #6 $139.54   4.686%   $146.0788   $146.08   $146.10   $146.10  
  Purchase #7 $107.59   6.280%   $114.3467   $114.35   $114.35   $114.30  
  7 purchase totals = $1,277.18       $1,337.5371   $1,337.53   $1,337.60   $1,337.50