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 $211.61   6.693%   $225.7731   $225.77   $225.75   $225.80  
  Purchase #2 $225.53   9.241%   $246.3712   $246.37   $246.35   $246.40  
  Purchase #3 $12.74   5.828%   $13.4825   $13.48   $13.50   $13.50  
  Purchase #4 $99.64   13.285%   $112.8772   $112.88   $112.90   $112.90  
  Purchase #5 $157.91   8.596%   $171.4839   $171.48   $171.50   $171.50  
  Purchase #6 $182.76   5.189%   $192.2434   $192.24   $192.25   $192.20  
  Purchase #7 $29.47   4.298%   $30.7366   $30.74   $30.75   $30.70  
  7 purchase totals = $919.66       $992.9679   $992.96   $993.00   $993.00