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	$127.45	8.662%	$138.4897	$138.49	$138.50	$138.50
Purchase #2	$101.62	9.585%	$111.3603	$111.36	$111.35	$111.40
Purchase #3	$243.50	6.333%	$258.9209	$258.92	$258.90	$258.90
Purchase #4	$44.28	13.339%	$50.1865	$50.19	$50.20	$50.20
Purchase #5	$140.89	9.235%	$153.9012	$153.90	$153.90	$153.90
Purchase #6	$61.84	3.677%	$64.1139	$64.11	$64.10	$64.10
Purchase #7	$245.58	10.181%	$270.5825	$270.58	$270.60	$270.60
7 purchase totals =	$965.16		$1,047.5550	$1,047.55	$1,047.55	$1,047.60