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	$45.74	5.620%	$48.3106	$48.31	$48.30	$48.30
Purchase #2	$153.92	3.337%	$159.0563	$159.06	$159.05	$159.10
Purchase #3	$172.74	13.616%	$196.2603	$196.26	$196.25	$196.30
Purchase #4	$40.55	4.819%	$42.5041	$42.50	$42.50	$42.50
Purchase #5	$17.33	9.141%	$18.9141	$18.91	$18.90	$18.90
Purchase #6	$238.60	8.362%	$258.5517	$258.55	$258.55	$258.60
Purchase #7	$148.29	10.510%	$163.8753	$163.88	$163.90	$163.90
7 purchase totals =	$817.17		$887.4724	$887.47	$887.45	$887.60