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	$232.66	6.422%	$247.6014	$247.60	$247.60	$247.60
Purchase #2	$179.89	7.657%	$193.6642	$193.66	$193.65	$193.70
Purchase #3	$69.25	13.598%	$78.6666	$78.67	$78.65	$78.70
Purchase #4	$40.64	6.449%	$43.2609	$43.26	$43.25	$43.30
Purchase #5	$50.60	3.494%	$52.368	$52.37	$52.35	$52.40
Purchase #6	$43.61	6.388%	$46.3958	$46.40	$46.40	$46.40
Purchase #7	$105.62	12.179%	$118.4835	$118.48	$118.50	$118.50
7 purchase totals =	$722.27		$780.4404	$780.44	$780.40	$780.60