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 $209.42   8.143%   $226.4731   $226.47   $226.45   $226.50  
  Purchase #2 $33.45   3.516%   $34.6261   $34.63   $34.65   $34.60  
  Purchase #3 $40.68   5.661%   $42.9829   $42.98   $43.00   $43.00  
  Purchase #4 $69.58   9.685%   $76.3188   $76.32   $76.30   $76.30  
  Purchase #5 $80.68   4.626%   $84.4123   $84.41   $84.40   $84.40  
  Purchase #6 $119.55   5.351%   $125.9471   $125.95   $125.95   $125.90  
  Purchase #7 $125.45   4.185%   $130.7001   $130.70   $130.70   $130.70  
  7 purchase totals = $678.81       $721.4604   $721.46   $721.45   $721.40