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	$34.97	9.175%	$38.1785	$38.18	$38.20	$38.20
Purchase #2	$215.39	3.745%	$223.4564	$223.46	$223.45	$223.50
Purchase #3	$22.96	3.865%	$23.8474	$23.85	$23.85	$23.80
Purchase #4	$132.50	9.365%	$144.9086	$144.91	$144.90	$144.90
Purchase #5	$248.28	11.796%	$277.5671	$277.57	$277.55	$277.60
Purchase #6	$137.71	13.376%	$156.1301	$156.13	$156.15	$156.10
Purchase #7	$29.52	13.632%	$33.5442	$33.54	$33.55	$33.50
7 purchase totals =	$821.33		$897.6323	$897.64	$897.65	$897.60