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	$37.59	11.472%	$41.9023	$41.90	$41.90	$41.90
Purchase #2	$80.69	11.845%	$90.2477	$90.25	$90.25	$90.20
Purchase #3	$162.92	11.532%	$181.7079	$181.71	$181.70	$181.70
Purchase #4	$9.26	8.645%	$10.0605	$10.06	$10.05	$10.10
Purchase #5	$37.43	8.447%	$40.5917	$40.59	$40.60	$40.60
Purchase #6	$69.81	7.144%	$74.7972	$74.80	$74.80	$74.80
Purchase #7	$165.52	8.117%	$178.9553	$178.96	$178.95	$179.00
7 purchase totals =	$563.22		$618.2626	$618.27	$618.25	$618.30