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 $56.43   11.624%   $62.9894   $62.99   $63.00   $63.00  
  Purchase #2 $207.51   11.586%   $231.5521   $231.55   $231.55   $231.60  
  Purchase #3 $195.73   3.811%   $203.1893   $203.19   $203.20   $203.20  
  Purchase #4 $147.95   10.658%   $163.7185   $163.72   $163.70   $163.70  
  Purchase #5 $241.34   10.595%   $266.91   $266.91   $266.90   $266.90  
  Purchase #6 $217.70   5.767%   $230.2548   $230.25   $230.25   $230.30  
  Purchase #7 $208.29   12.186%   $233.6722   $233.67   $233.65   $233.70  
  7 purchase totals = $1,274.95       $1,392.2863   $1,392.28   $1,392.25   $1,392.40