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	$82.72	11.723%	$92.4173	$92.42	$92.40	$92.40
Purchase #2	$20.26	6.829%	$21.6436	$21.64	$21.65	$21.60
Purchase #3	$62.74	9.825%	$68.9042	$68.90	$68.90	$68.90
Purchase #4	$229.60	9.588%	$251.614	$251.61	$251.60	$251.60
Purchase #5	$107.83	3.781%	$111.9071	$111.91	$111.90	$111.90
Purchase #6	$183.52	13.319%	$207.963	$207.96	$207.95	$208.00
Purchase #7	$127.89	7.254%	$137.1671	$137.17	$137.15	$137.20
7 purchase totals =	$814.56		$891.6163	$891.61	$891.55	$891.60