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	$155.26	6.589%	$165.4901	$165.49	$165.50	$165.50
Purchase #2	$190.71	3.269%	$196.9443	$196.94	$196.95	$196.90
Purchase #3	$111.78	10.202%	$123.1838	$123.18	$123.20	$123.20
Purchase #4	$199.31	12.689%	$224.6004	$224.60	$224.60	$224.60
Purchase #5	$138.34	9.826%	$151.9333	$151.93	$151.95	$151.90
Purchase #6	$221.82	8.768%	$241.2692	$241.27	$241.25	$241.30
Purchase #7	$244.92	10.316%	$270.1859	$270.19	$270.20	$270.20
7 purchase totals =	$1,262.14		$1,373.6070	$1,373.60	$1,373.65	$1,373.60