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	$115.51	12.812%	$130.3091	$130.31	$130.30	$130.30
Purchase #2	$70.92	11.795%	$79.285	$79.29	$79.30	$79.30
Purchase #3	$163.75	5.689%	$173.0657	$173.07	$173.05	$173.10
Purchase #4	$180.33	5.209%	$189.7234	$189.72	$189.70	$189.70
Purchase #5	$152.60	13.511%	$173.2178	$173.22	$173.20	$173.20
Purchase #6	$114.67	11.163%	$127.4706	$127.47	$127.45	$127.50
Purchase #7	$92.69	13.778%	$105.4608	$105.46	$105.45	$105.50
7 purchase totals =	$890.47		$978.5324	$978.54	$978.45	$978.60