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	$83.99	4.193%	$87.5117	$87.51	$87.50	$87.50
Purchase #2	$50.93	4.447%	$53.1949	$53.19	$53.20	$53.20
Purchase #3	$30.33	4.622%	$31.7319	$31.73	$31.75	$31.70
Purchase #4	$62.56	9.419%	$68.4525	$68.45	$68.45	$68.50
Purchase #5	$230.37	10.420%	$254.3746	$254.37	$254.35	$254.40
Purchase #6	$107.92	3.233%	$111.4091	$111.41	$111.40	$111.40
Purchase #7	$53.71	13.771%	$61.1064	$61.11	$61.10	$61.10
7 purchase totals =	$619.81		$667.7811	$667.77	$667.75	$667.80