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	$107.84	3.627%	$111.7514	$111.75	$111.75	$111.80
Purchase #2	$35.89	12.502%	$40.377	$40.38	$40.40	$40.40
Purchase #3	$52.54	13.191%	$59.4706	$59.47	$59.45	$59.50
Purchase #4	$196.85	7.225%	$211.0724	$211.07	$211.05	$211.10
Purchase #5	$74.35	6.851%	$79.4437	$79.44	$79.45	$79.40
Purchase #6	$199.93	7.394%	$214.7128	$214.71	$214.70	$214.70
Purchase #7	$113.57	8.230%	$122.9168	$122.92	$122.90	$122.90
7 purchase totals =	$780.97		$839.7447	$839.74	$839.70	$839.80