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	$16.71	6.658%	$17.8226	$17.82	$17.80	$17.80
Purchase #2	$236.40	11.459%	$263.4891	$263.49	$263.50	$263.50
Purchase #3	$171.27	12.232%	$192.2197	$192.22	$192.20	$192.20
Purchase #4	$236.81	7.716%	$255.0823	$255.08	$255.10	$255.10
Purchase #5	$171.92	10.751%	$190.4031	$190.40	$190.40	$190.40
Purchase #6	$130.65	9.138%	$142.5888	$142.59	$142.60	$142.60
Purchase #7	$105.51	5.391%	$111.198	$111.20	$111.20	$111.20
7 purchase totals =	$1,069.27		$1,172.8036	$1,172.80	$1,172.80	$1,172.80