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	$147.90	13.196%	$167.4169	$167.42	$167.40	$167.40
Purchase #2	$71.79	9.311%	$78.4744	$78.47	$78.45	$78.50
Purchase #3	$224.50	8.534%	$243.6588	$243.66	$243.65	$243.70
Purchase #4	$72.78	7.634%	$78.336	$78.34	$78.35	$78.30
Purchase #5	$233.29	8.857%	$253.9525	$253.95	$253.95	$254.00
Purchase #6	$211.77	4.532%	$221.3674	$221.37	$221.35	$221.40
Purchase #7	$53.70	4.414%	$56.0703	$56.07	$56.05	$56.10
7 purchase totals =	$1,015.73		$1,099.2763	$1,099.28	$1,099.20	$1,099.40