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	$143.91	6.543%	$153.326	$153.33	$153.35	$153.30
Purchase #2	$46.84	6.424%	$49.849	$49.85	$49.85	$49.80
Purchase #3	$33.89	11.814%	$37.8938	$37.89	$37.90	$37.90
Purchase #4	$58.70	13.347%	$66.5347	$66.53	$66.55	$66.50
Purchase #5	$49.38	9.239%	$53.9422	$53.94	$53.95	$53.90
Purchase #6	$38.89	4.333%	$40.5751	$40.58	$40.60	$40.60
Purchase #7	$164.68	12.185%	$184.7463	$184.75	$184.75	$184.70
7 purchase totals =	$536.29		$586.8671	$586.87	$586.95	$586.70