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	$155.80	7.540%	$167.5473	$167.55	$167.55	$167.50
Purchase #2	$228.61	12.793%	$257.8561	$257.86	$257.85	$257.90
Purchase #3	$80.52	8.651%	$87.4858	$87.49	$87.50	$87.50
Purchase #4	$242.72	5.177%	$255.2856	$255.29	$255.30	$255.30
Purchase #5	$224.89	6.130%	$238.6758	$238.68	$238.70	$238.70
Purchase #6	$116.91	11.553%	$130.4166	$130.42	$130.40	$130.40
Purchase #7	$48.64	7.842%	$52.4543	$52.45	$52.45	$52.50
7 purchase totals =	$1,098.09		$1,189.7215	$1,189.74	$1,189.75	$1,189.80