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	$40.27	13.727%	$45.7979	$45.80	$45.80	$45.80
Purchase #2	$242.35	11.851%	$271.0709	$271.07	$271.05	$271.10
Purchase #3	$151.55	11.525%	$169.0161	$169.02	$169.00	$169.00
Purchase #4	$221.77	3.299%	$229.0862	$229.09	$229.10	$229.10
Purchase #5	$48.62	10.501%	$53.7256	$53.73	$53.75	$53.70
Purchase #6	$187.46	9.161%	$204.6332	$204.63	$204.65	$204.60
Purchase #7	$43.45	4.658%	$45.4739	$45.47	$45.45	$45.50
7 purchase totals =	$935.47		$1,018.8038	$1,018.81	$1,018.80	$1,018.80