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 $114.83   9.551%   $125.7974   $125.80   $125.80   $125.80  
  Purchase #2 $96.30   8.308%   $104.3006   $104.30   $104.30   $104.30  
  Purchase #3 $16.57   9.686%   $18.175   $18.18   $18.20   $18.20  
  Purchase #4 $140.83   7.691%   $151.6612   $151.66   $151.65   $151.70  
  Purchase #5 $25.73   3.395%   $26.6035   $26.60   $26.60   $26.60  
  Purchase #6 $233.32   8.104%   $252.2283   $252.23   $252.25   $252.20  
  Purchase #7 $95.57   6.137%   $101.4351   $101.44   $101.45   $101.40  
  7 purchase totals = $723.15       $780.2011   $780.21   $780.25   $780.20