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	$90.89	10.495%	$100.4289	$100.43	$100.45	$100.40
Purchase #2	$71.31	3.423%	$73.7509	$73.75	$73.75	$73.80
Purchase #3	$173.71	13.651%	$197.4232	$197.42	$197.40	$197.40
Purchase #4	$54.39	10.638%	$60.176	$60.18	$60.20	$60.20
Purchase #5	$127.93	8.794%	$139.1802	$139.18	$139.20	$139.20
Purchase #6	$158.73	8.378%	$172.0284	$172.03	$172.05	$172.00
Purchase #7	$219.56	5.421%	$231.4623	$231.46	$231.45	$231.50
7 purchase totals =	$896.52		$974.4499	$974.45	$974.50	$974.50