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	$54.77	5.127%	$57.5781	$57.58	$57.60	$57.60
Purchase #2	$191.81	10.467%	$211.8868	$211.89	$211.90	$211.90
Purchase #3	$49.62	5.602%	$52.3997	$52.40	$52.40	$52.40
Purchase #4	$153.49	3.238%	$158.46	$158.46	$158.45	$158.50
Purchase #5	$53.46	9.438%	$58.5056	$58.51	$58.50	$58.50
Purchase #6	$152.96	13.601%	$173.7641	$173.76	$173.75	$173.80
Purchase #7	$61.42	9.479%	$67.242	$67.24	$67.25	$67.20
7 purchase totals =	$717.53		$779.8363	$779.84	$779.85	$779.90