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 $83.42   10.869%   $92.4869   $92.49   $92.50   $92.50  
  Purchase #2 $142.89   10.328%   $157.6477   $157.65   $157.65   $157.60  
  Purchase #3 $124.91   4.788%   $130.8907   $130.89   $130.90   $130.90  
  Purchase #4 $242.82   7.683%   $261.4759   $261.48   $261.50   $261.50  
  Purchase #5 $65.89   6.695%   $70.3013   $70.30   $70.30   $70.30  
  Purchase #6 $88.51   8.456%   $95.9944   $95.99   $96.00   $96.00  
  Purchase #7 $236.37   10.807%   $261.9145   $261.91   $261.90   $261.90  
  7 purchase totals = $984.81       $1,070.7114   $1,070.71   $1,070.75   $1,070.70