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	$153.35	5.827%	$162.2857	$162.29	$162.30	$162.30
Purchase #2	$34.69	7.382%	$37.2508	$37.25	$37.25	$37.30
Purchase #3	$13.40	11.668%	$14.9635	$14.96	$14.95	$15.00
Purchase #4	$85.36	12.719%	$96.2169	$96.22	$96.20	$96.20
Purchase #5	$73.28	7.331%	$78.6522	$78.65	$78.65	$78.70
Purchase #6	$12.56	7.857%	$13.5468	$13.55	$13.55	$13.50
Purchase #7	$134.39	13.727%	$152.8377	$152.84	$152.85	$152.80
7 purchase totals =	$507.03		$555.7536	$555.76	$555.75	$555.80