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 $105.49   8.603%   $114.5653   $114.57   $114.55   $114.60  
  Purchase #2 $233.71   3.869%   $242.7522   $242.75   $242.75   $242.80  
  Purchase #3 $112.36   11.403%   $125.1724   $125.17   $125.15   $125.20  
  Purchase #4 $31.97   10.160%   $35.2182   $35.22   $35.20   $35.20  
  Purchase #5 $167.49   8.626%   $181.9377   $181.94   $181.95   $181.90  
  Purchase #6 $24.53   7.612%   $26.3972   $26.40   $26.40   $26.40  
  Purchase #7 $229.65   4.495%   $239.9728   $239.97   $239.95   $240.00  
  7 purchase totals = $905.20       $966.0158   $966.02   $965.95   $966.10