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	$139.59	6.120%	$148.1329	$148.13	$148.15	$148.10
Purchase #2	$214.40	11.633%	$239.3412	$239.34	$239.35	$239.30
Purchase #3	$134.47	6.654%	$143.4176	$143.42	$143.40	$143.40
Purchase #4	$33.96	10.672%	$37.5842	$37.58	$37.60	$37.60
Purchase #5	$49.44	10.200%	$54.4829	$54.48	$54.50	$54.50
Purchase #6	$79.35	10.450%	$87.6421	$87.64	$87.65	$87.60
Purchase #7	$170.89	10.431%	$188.7155	$188.72	$188.70	$188.70
7 purchase totals =	$822.10		$899.3164	$899.31	$899.35	$899.20