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 $162.44   6.664%   $173.265   $173.27   $173.25   $173.30  
  Purchase #2 $239.45   7.716%   $257.926   $257.93   $257.95   $257.90  
  Purchase #3 $187.94   9.716%   $206.2003   $206.20   $206.20   $206.20  
  Purchase #4 $49.98   3.750%   $51.8543   $51.85   $51.85   $51.90  
  Purchase #5 $234.37   7.699%   $252.4141   $252.41   $252.40   $252.40  
  Purchase #6 $150.53   5.134%   $158.2582   $158.26   $158.25   $158.30  
  Purchase #7 $238.58   4.189%   $248.5741   $248.57   $248.55   $248.60  
  7 purchase totals = $1,263.29       $1,348.4920   $1,348.49   $1,348.45   $1,348.60