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	$167.50	8.231%	$181.2869	$181.29	$181.30	$181.30
Purchase #2	$43.66	4.422%	$45.5906	$45.59	$45.60	$45.60
Purchase #3	$37.28	12.826%	$42.0615	$42.06	$42.05	$42.10
Purchase #4	$87.60	11.367%	$97.5575	$97.56	$97.55	$97.60
Purchase #5	$61.99	7.296%	$66.5128	$66.51	$66.50	$66.50
Purchase #6	$133.64	11.474%	$148.9739	$148.97	$148.95	$149.00
Purchase #7	$60.33	7.292%	$64.7293	$64.73	$64.75	$64.70
7 purchase totals =	$592.00		$646.7125	$646.71	$646.70	$646.80