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	$88.47	12.392%	$99.4332	$99.43	$99.45	$99.40
Purchase #2	$58.86	10.591%	$65.0939	$65.09	$65.10	$65.10
Purchase #3	$50.64	6.176%	$53.7675	$53.77	$53.75	$53.80
Purchase #4	$173.58	9.701%	$190.419	$190.42	$190.40	$190.40
Purchase #5	$97.31	11.278%	$108.2846	$108.28	$108.30	$108.30
Purchase #6	$141.91	4.497%	$148.2917	$148.29	$148.30	$148.30
Purchase #7	$89.95	11.103%	$99.9371	$99.94	$99.95	$99.90
7 purchase totals =	$700.72		$765.2270	$765.22	$765.25	$765.20