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	$147.72	5.546%	$155.9126	$155.91	$155.90	$155.90
Purchase #2	$177.56	6.567%	$189.2204	$189.22	$189.20	$189.20
Purchase #3	$59.75	11.474%	$66.6057	$66.61	$66.60	$66.60
Purchase #4	$62.92	13.652%	$71.5098	$71.51	$71.50	$71.50
Purchase #5	$35.70	13.184%	$40.4067	$40.41	$40.40	$40.40
Purchase #6	$226.58	13.188%	$256.4614	$256.46	$256.45	$256.50
Purchase #7	$127.52	3.838%	$132.4142	$132.41	$132.40	$132.40
7 purchase totals =	$837.75		$912.5308	$912.53	$912.45	$912.50