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 $77.92   11.133%   $86.5948   $86.59   $86.60   $86.60  
  Purchase #2 $128.43   9.501%   $140.6321   $140.63   $140.65   $140.60  
  Purchase #3 $46.99   3.348%   $48.5632   $48.56   $48.55   $48.60  
  Purchase #4 $214.59   13.835%   $244.2785   $244.28   $244.30   $244.30  
  Purchase #5 $210.94   6.226%   $224.0731   $224.07   $224.05   $224.10  
  Purchase #6 $64.43   4.720%   $67.4711   $67.47   $67.45   $67.50  
  Purchase #7 $15.91   5.763%   $16.8269   $16.83   $16.85   $16.80  
  7 purchase totals = $759.21       $828.4397   $828.43   $828.45   $828.50