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	$138.89	5.339%	$146.3053	$146.31	$146.30	$146.30
Purchase #2	$202.43	6.293%	$215.1689	$215.17	$215.15	$215.20
Purchase #3	$190.48	5.198%	$200.3812	$200.38	$200.40	$200.40
Purchase #4	$182.72	4.177%	$190.3522	$190.35	$190.35	$190.40
Purchase #5	$152.82	10.429%	$168.7576	$168.76	$168.75	$168.80
Purchase #6	$139.53	13.813%	$158.8033	$158.80	$158.80	$158.80
Purchase #7	$132.86	5.786%	$140.5473	$140.55	$140.55	$140.50
7 purchase totals =	$1,139.73		$1,220.3158	$1,220.32	$1,220.30	$1,220.40