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	$147.30	12.795%	$166.147	$166.15	$166.15	$166.10
Purchase #2	$81.62	7.425%	$87.6803	$87.68	$87.70	$87.70
Purchase #3	$38.77	4.296%	$40.4356	$40.44	$40.45	$40.40
Purchase #4	$105.51	10.668%	$116.7658	$116.77	$116.75	$116.80
Purchase #5	$49.41	12.480%	$55.5764	$55.58	$55.60	$55.60
Purchase #6	$118.61	7.822%	$127.8877	$127.89	$127.90	$127.90
Purchase #7	$65.84	3.767%	$68.3202	$68.32	$68.30	$68.30
7 purchase totals =	$607.06		$662.8130	$662.83	$662.85	$662.80