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	$48.45	11.545%	$54.0436	$54.04	$54.05	$54.00
Purchase #2	$71.90	9.337%	$78.6133	$78.61	$78.60	$78.60
Purchase #3	$67.86	13.133%	$76.7721	$76.77	$76.75	$76.80
Purchase #4	$90.39	11.533%	$100.8147	$100.81	$100.80	$100.80
Purchase #5	$147.25	13.468%	$167.0816	$167.08	$167.10	$167.10
Purchase #6	$77.53	4.252%	$80.8266	$80.83	$80.85	$80.80
Purchase #7	$242.81	7.388%	$260.7488	$260.75	$260.75	$260.70
7 purchase totals =	$746.19		$818.9007	$818.89	$818.90	$818.80