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 $24.87   5.198%   $26.1627   $26.16   $26.15   $26.20  
  Purchase #2 $185.50   11.409%   $206.6637   $206.66   $206.65   $206.70  
  Purchase #3 $231.66   5.588%   $244.6052   $244.61   $244.60   $244.60  
  Purchase #4 $210.79   3.219%   $217.5753   $217.58   $217.60   $217.60  
  Purchase #5 $66.82   4.657%   $69.9318   $69.93   $69.95   $69.90  
  Purchase #6 $222.52   3.392%   $230.0679   $230.07   $230.05   $230.10  
  Purchase #7 $233.25   6.406%   $248.192   $248.19   $248.20   $248.20  
  7 purchase totals = $1,175.41       $1,243.1986   $1,243.20   $1,243.20   $1,243.30