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	$157.52	5.833%	$166.7081	$166.71	$166.70	$166.70
Purchase #2	$109.48	12.293%	$122.9384	$122.94	$122.95	$122.90
Purchase #3	$234.77	11.224%	$261.1206	$261.12	$261.10	$261.10
Purchase #4	$56.78	5.404%	$59.8484	$59.85	$59.85	$59.80
Purchase #5	$162.60	6.169%	$172.6308	$172.63	$172.65	$172.60
Purchase #6	$224.64	7.396%	$241.2544	$241.25	$241.25	$241.30
Purchase #7	$225.36	13.723%	$256.2862	$256.29	$256.30	$256.30
7 purchase totals =	$1,171.15		$1,280.7869	$1,280.79	$1,280.80	$1,280.70