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 $197.77   12.350%   $222.1946   $222.19   $222.20   $222.20  
  Purchase #2 $66.26   10.707%   $73.3545   $73.35   $73.35   $73.40  
  Purchase #3 $59.99   5.105%   $63.0525   $63.05   $63.05   $63.10  
  Purchase #4 $207.90   9.620%   $227.9   $227.90   $227.90   $227.90  
  Purchase #5 $37.71   6.548%   $40.1793   $40.18   $40.20   $40.20  
  Purchase #6 $22.31   8.860%   $24.2867   $24.29   $24.30   $24.30  
  Purchase #7 $126.44   6.675%   $134.8799   $134.88   $134.90   $134.90  
  7 purchase totals = $718.38       $785.8475   $785.84   $785.90   $786.00