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 $83.49   13.243%   $94.5466   $94.55   $94.55   $94.50  
  Purchase #2 $68.39   6.342%   $72.7273   $72.73   $72.75   $72.70  
  Purchase #3 $234.68   11.671%   $262.0695   $262.07   $262.05   $262.10  
  Purchase #4 $249.70   6.848%   $266.7995   $266.80   $266.80   $266.80  
  Purchase #5 $35.31   7.689%   $38.025   $38.03   $38.05   $38.00  
  Purchase #6 $72.50   3.239%   $74.8483   $74.85   $74.85   $74.80  
  Purchase #7 $29.42   4.807%   $30.8342   $30.83   $30.85   $30.80  
  7 purchase totals = $773.49       $839.8504   $839.86   $839.90   $839.70