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 $250.35   4.253%   $260.9974   $261.00   $261.00   $261.00  
  Purchase #2 $49.31   11.159%   $54.8125   $54.81   $54.80   $54.80  
  Purchase #3 $113.26   10.785%   $125.4751   $125.48   $125.50   $125.50  
  Purchase #4 $86.34   9.326%   $94.3921   $94.39   $94.40   $94.40  
  Purchase #5 $207.25   6.246%   $220.1948   $220.19   $220.20   $220.20  
  Purchase #6 $167.30   13.720%   $190.2536   $190.25   $190.25   $190.30  
  Purchase #7 $142.43   6.306%   $151.4116   $151.41   $151.40   $151.40  
  7 purchase totals = $1,016.24       $1,097.5371   $1,097.53   $1,097.55   $1,097.60