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 $112.48   13.754%   $127.9505   $127.95   $127.95   $128.00  
  Purchase #2 $6.73   4.380%   $7.0248   $7.02   $7.00   $7.00  
  Purchase #3 $125.40   3.745%   $130.0962   $130.10   $130.10   $130.10  
  Purchase #4 $178.97   4.769%   $187.5051   $187.51   $187.50   $187.50  
  Purchase #5 $203.95   3.569%   $211.229   $211.23   $211.25   $211.20  
  Purchase #6 $125.45   9.406%   $137.2498   $137.25   $137.25   $137.20  
  Purchase #7 $203.74   11.720%   $227.6183   $227.62   $227.60   $227.60  
  7 purchase totals = $956.72       $1,028.6737   $1,028.68   $1,028.65   $1,028.60