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	$146.43	12.354%	$164.52	$164.52	$164.50	$164.50
Purchase #2	$127.38	9.173%	$139.0646	$139.06	$139.05	$139.10
Purchase #3	$99.47	3.765%	$103.215	$103.22	$103.20	$103.20
Purchase #4	$23.83	10.156%	$26.2502	$26.25	$26.25	$26.30
Purchase #5	$167.42	4.822%	$175.493	$175.49	$175.50	$175.50
Purchase #6	$71.92	12.174%	$80.6755	$80.68	$80.70	$80.70
Purchase #7	$190.82	6.109%	$202.4772	$202.48	$202.50	$202.50
7 purchase totals =	$827.27		$891.6955	$891.70	$891.70	$891.80