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 $58.53   4.162%   $60.966   $60.97   $60.95   $61.00  
  Purchase #2 $128.80   3.840%   $133.7459   $133.75   $133.75   $133.70  
  Purchase #3 $233.37   8.553%   $253.3301   $253.33   $253.35   $253.30  
  Purchase #4 $40.41   13.461%   $45.8496   $45.85   $45.85   $45.80  
  Purchase #5 $33.76   5.510%   $35.6202   $35.62   $35.60   $35.60  
  Purchase #6 $196.69   9.354%   $215.0884   $215.09   $215.10   $215.10  
  Purchase #7 $37.41   12.252%   $41.9935   $41.99   $42.00   $42.00  
  7 purchase totals = $728.97       $786.5937   $786.60   $786.60   $786.50