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 $158.27   11.681%   $176.7575   $176.76   $176.75   $176.80  
  Purchase #2 $154.89   8.493%   $168.0448   $168.04   $168.05   $168.00  
  Purchase #3 $162.47   10.206%   $179.0517   $179.05   $179.05   $179.10  
  Purchase #4 $237.84   10.649%   $263.1676   $263.17   $263.15   $263.20  
  Purchase #5 $125.57   12.834%   $141.6857   $141.69   $141.70   $141.70  
  Purchase #6 $95.76   10.216%   $105.5428   $105.54   $105.55   $105.50  
  Purchase #7 $41.45   13.377%   $46.9948   $46.99   $47.00   $47.00  
  7 purchase totals = $976.25       $1,081.2449   $1,081.24   $1,081.25   $1,081.30