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 $242.49   7.852%   $261.5303   $261.53   $261.55   $261.50  
  Purchase #2 $180.97   8.491%   $196.3362   $196.34   $196.35   $196.30  
  Purchase #3 $96.88   11.293%   $107.8207   $107.82   $107.80   $107.80  
  Purchase #4 $153.68   10.212%   $169.3738   $169.37   $169.35   $169.40  
  Purchase #5 $139.62   3.643%   $144.7064   $144.71   $144.70   $144.70  
  Purchase #6 $75.97   11.670%   $84.8357   $84.84   $84.85   $84.80  
  Purchase #7 $56.62   6.662%   $60.392   $60.39   $60.40   $60.40  
  7 purchase totals = $946.23       $1,024.9951   $1,025.00   $1,025.00   $1,024.90