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 $60.88   12.159%   $68.2824   $68.28   $68.30   $68.30  
  Purchase #2 $107.79   7.272%   $115.6285   $115.63   $115.65   $115.60  
  Purchase #3 $159.83   3.223%   $164.9813   $164.98   $165.00   $165.00  
  Purchase #4 $38.59   6.126%   $40.954   $40.95   $40.95   $41.00  
  Purchase #5 $102.73   7.496%   $110.4306   $110.43   $110.45   $110.40  
  Purchase #6 $16.58   7.400%   $17.8069   $17.81   $17.80   $17.80  
  Purchase #7 $187.64   5.639%   $198.221   $198.22   $198.20   $198.20  
  7 purchase totals = $674.04       $716.3047   $716.30   $716.35   $716.30