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	$125.68	9.724%	$137.9011	$137.90	$137.90	$137.90
Purchase #2	$148.70	9.152%	$162.309	$162.31	$162.30	$162.30
Purchase #3	$64.90	4.867%	$68.0587	$68.06	$68.05	$68.10
Purchase #4	$152.33	11.470%	$169.8023	$169.80	$169.80	$169.80
Purchase #5	$128.27	13.688%	$145.8276	$145.83	$145.85	$145.80
Purchase #6	$94.26	6.707%	$100.582	$100.58	$100.60	$100.60
Purchase #7	$122.33	8.240%	$132.41	$132.41	$132.40	$132.40
7 purchase totals =	$836.47		$916.8907	$916.89	$916.90	$916.90