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 $166.58   9.730%   $182.7882   $182.79   $182.80   $182.80  
  Purchase #2 $204.77   4.683%   $214.3594   $214.36   $214.35   $214.40  
  Purchase #3 $247.78   6.198%   $263.1374   $263.14   $263.15   $263.10  
  Purchase #4 $237.27   4.784%   $248.621   $248.62   $248.60   $248.60  
  Purchase #5 $231.45   4.852%   $242.68   $242.68   $242.70   $242.70  
  Purchase #6 $113.92   7.497%   $122.4606   $122.46   $122.45   $122.50  
  Purchase #7 $71.53   5.337%   $75.3476   $75.35   $75.35   $75.30  
  7 purchase totals = $1,273.30       $1,349.3942   $1,349.40   $1,349.40   $1,349.40