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 $246.53   6.510%   $262.5791   $262.58   $262.60   $262.60  
  Purchase #2 $214.54   12.191%   $240.6946   $240.69   $240.70   $240.70  
  Purchase #3 $71.58   9.252%   $78.2026   $78.20   $78.20   $78.20  
  Purchase #4 $116.91   7.667%   $125.8735   $125.87   $125.85   $125.90  
  Purchase #5 $65.91   9.474%   $72.1543   $72.15   $72.15   $72.20  
  Purchase #6 $192.70   11.477%   $214.8162   $214.82   $214.80   $214.80  
  Purchase #7 $163.99   13.261%   $185.7367   $185.74   $185.75   $185.70  
  7 purchase totals = $1,072.16       $1,180.0570   $1,180.05   $1,180.05   $1,180.10