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 $26.63   12.159%   $29.8679   $29.87   $29.85   $29.90  
  Purchase #2 $193.49   10.682%   $214.1586   $214.16   $214.15   $214.20  
  Purchase #3 $33.81   5.687%   $35.7328   $35.73   $35.75   $35.70  
  Purchase #4 $29.35   7.751%   $31.6249   $31.62   $31.60   $31.60  
  Purchase #5 $92.34   4.457%   $96.4556   $96.46   $96.45   $96.50  
  Purchase #6 $211.74   13.818%   $240.9982   $241.00   $241.00   $241.00  
  Purchase #7 $71.99   4.267%   $75.0618   $75.06   $75.05   $75.10  
  7 purchase totals = $659.35       $723.8998   $723.90   $723.85   $724.00