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	$215.42	6.539%	$229.5063	$229.51	$229.50	$229.50
Purchase #2	$80.43	11.563%	$89.7301	$89.73	$89.75	$89.70
Purchase #3	$153.29	3.695%	$158.9541	$158.95	$158.95	$159.00
Purchase #4	$172.77	9.773%	$189.6548	$189.65	$189.65	$189.70
Purchase #5	$115.92	6.285%	$123.2056	$123.21	$123.20	$123.20
Purchase #6	$130.87	11.719%	$146.2067	$146.21	$146.20	$146.20
Purchase #7	$56.79	8.450%	$61.5888	$61.59	$61.60	$61.60
7 purchase totals =	$925.49		$998.8464	$998.85	$998.85	$998.90