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 $221.32   10.813%   $245.2513   $245.25   $245.25   $245.30  
  Purchase #2 $219.46   13.420%   $248.9115   $248.91   $248.90   $248.90  
  Purchase #3 $220.37   7.181%   $236.1948   $236.19   $236.20   $236.20  
  Purchase #4 $60.82   13.517%   $69.041   $69.04   $69.05   $69.00  
  Purchase #5 $77.48   13.180%   $87.6919   $87.69   $87.70   $87.70  
  Purchase #6 $9.26   3.634%   $9.5965   $9.60   $9.60   $9.60  
  Purchase #7 $169.77   7.448%   $182.4145   $182.41   $182.40   $182.40  
  7 purchase totals = $978.48       $1,079.1015   $1,079.09   $1,079.10   $1,079.10