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 $234.77   11.342%   $261.3976   $261.40   $261.40   $261.40  
  Purchase #2 $44.43   11.254%   $49.4302   $49.43   $49.45   $49.40  
  Purchase #3 $53.97   10.125%   $59.4345   $59.43   $59.45   $59.40  
  Purchase #4 $72.65   4.460%   $75.8902   $75.89   $75.90   $75.90  
  Purchase #5 $116.90   6.578%   $124.5897   $124.59   $124.60   $124.60  
  Purchase #6 $234.91   7.648%   $252.8759   $252.88   $252.90   $252.90  
  Purchase #7 $125.36   7.172%   $134.3508   $134.35   $134.35   $134.40  
  7 purchase totals = $882.99       $957.9689   $957.97   $958.05   $958.00