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 $126.68   12.554%   $142.5834   $142.58   $142.60   $142.60  
  Purchase #2 $60.70   6.382%   $64.5739   $64.57   $64.55   $64.60  
  Purchase #3 $96.64   9.422%   $105.7454   $105.75   $105.75   $105.70  
  Purchase #4 $192.80   4.169%   $200.8378   $200.84   $200.85   $200.80  
  Purchase #5 $212.58   11.565%   $237.1649   $237.16   $237.15   $237.20  
  Purchase #6 $227.57   9.105%   $248.2902   $248.29   $248.30   $248.30  
  Purchase #7 $65.76   13.112%   $74.3825   $74.38   $74.40   $74.40  
  7 purchase totals = $982.73       $1,073.5781   $1,073.57   $1,073.60   $1,073.60