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	$16.63	10.472%	$18.3715	$18.37	$18.35	$18.40
Purchase #2	$152.27	3.467%	$157.5492	$157.55	$157.55	$157.50
Purchase #3	$179.48	11.711%	$200.4989	$200.50	$200.50	$200.50
Purchase #4	$122.72	8.146%	$132.7168	$132.72	$132.70	$132.70
Purchase #5	$208.57	3.327%	$215.5091	$215.51	$215.50	$215.50
Purchase #6	$204.49	5.865%	$216.4833	$216.48	$216.50	$216.50
Purchase #7	$123.72	7.532%	$133.0386	$133.04	$133.05	$133.00
7 purchase totals =	$1,007.88		$1,074.1674	$1,074.17	$1,074.15	$1,074.10