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	$111.99	5.721%	$118.3969	$118.40	$118.40	$118.40
Purchase #2	$160.71	13.645%	$182.6389	$182.64	$182.65	$182.60
Purchase #3	$99.25	5.246%	$104.4567	$104.46	$104.45	$104.50
Purchase #4	$74.51	6.824%	$79.5946	$79.59	$79.60	$79.60
Purchase #5	$129.29	13.235%	$146.4015	$146.40	$146.40	$146.40
Purchase #6	$53.37	3.297%	$55.1296	$55.13	$55.15	$55.10
Purchase #7	$108.70	13.702%	$123.5941	$123.59	$123.60	$123.60
7 purchase totals =	$737.82		$810.2123	$810.21	$810.25	$810.20