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 $35.87   7.317%   $38.4946   $38.49   $38.50   $38.50  
  Purchase #2 $200.83   12.113%   $225.1565   $225.16   $225.15   $225.20  
  Purchase #3 $248.37   5.662%   $262.4327   $262.43   $262.45   $262.40  
  Purchase #4 $237.34   13.155%   $268.5621   $268.56   $268.55   $268.60  
  Purchase #5 $32.86   13.812%   $37.3986   $37.40   $37.40   $37.40  
  Purchase #6 $63.99   8.293%   $69.2967   $69.30   $69.30   $69.30  
  Purchase #7 $249.68   6.398%   $265.6545   $265.65   $265.65   $265.70  
  7 purchase totals = $1,068.94       $1,166.9957   $1,166.99   $1,167.00   $1,167.10