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	$99.55	6.231%	$105.753	$105.75	$105.75	$105.80
Purchase #2	$214.74	13.526%	$243.7857	$243.79	$243.80	$243.80
Purchase #3	$59.88	3.151%	$61.7668	$61.77	$61.75	$61.80
Purchase #4	$165.38	4.157%	$172.2548	$172.25	$172.25	$172.30
Purchase #5	$120.60	8.244%	$130.5423	$130.54	$130.55	$130.50
Purchase #6	$38.50	4.593%	$40.2683	$40.27	$40.25	$40.30
Purchase #7	$135.28	6.685%	$144.3235	$144.32	$144.30	$144.30
7 purchase totals =	$833.93		$898.6944	$898.69	$898.65	$898.80