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 $40.63   4.770%   $42.5681   $42.57   $42.55   $42.60  
  Purchase #2 $137.63   4.480%   $143.7958   $143.80   $143.80   $143.80  
  Purchase #3 $192.97   3.865%   $200.4283   $200.43   $200.45   $200.40  
  Purchase #4 $192.42   13.328%   $218.0657   $218.07   $218.05   $218.10  
  Purchase #5 $48.48   5.345%   $51.0713   $51.07   $51.05   $51.10  
  Purchase #6 $35.62   12.689%   $40.1398   $40.14   $40.15   $40.10  
  Purchase #7 $23.77   10.825%   $26.3431   $26.34   $26.35   $26.30  
  7 purchase totals = $671.52       $722.4121   $722.42   $722.40   $722.40