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	$81.41	6.600%	$86.7831	$86.78	$86.80	$86.80
Purchase #2	$137.63	11.858%	$153.9502	$153.95	$153.95	$154.00
Purchase #3	$207.70	11.334%	$231.2407	$231.24	$231.25	$231.20
Purchase #4	$97.80	13.602%	$111.1028	$111.10	$111.10	$111.10
Purchase #5	$61.67	11.109%	$68.5209	$68.52	$68.50	$68.50
Purchase #6	$140.67	4.301%	$146.7202	$146.72	$146.70	$146.70
Purchase #7	$214.39	11.240%	$238.4874	$238.49	$238.50	$238.50
7 purchase totals =	$941.27		$1,036.8053	$1,036.80	$1,036.80	$1,036.80