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 $210.33   5.838%   $222.6091   $222.61   $222.60   $222.60  
  Purchase #2 $96.35   3.359%   $99.5864   $99.59   $99.60   $99.60  
  Purchase #3 $101.56   10.513%   $112.237   $112.24   $112.25   $112.20  
  Purchase #4 $115.26   13.796%   $131.1613   $131.16   $131.15   $131.20  
  Purchase #5 $96.63   3.409%   $99.9241   $99.92   $99.90   $99.90  
  Purchase #6 $133.77   7.508%   $143.8135   $143.81   $143.80   $143.80  
  Purchase #7 $208.25   4.405%   $217.4234   $217.42   $217.40   $217.40  
  7 purchase totals = $962.15       $1,026.7548   $1,026.75   $1,026.70   $1,026.70