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	$108.28	3.272%	$111.8229	$111.82	$111.80	$111.80
Purchase #2	$75.43	10.149%	$83.0854	$83.09	$83.10	$83.10
Purchase #3	$181.84	10.449%	$200.8405	$200.84	$200.85	$200.80
Purchase #4	$189.34	5.836%	$200.3899	$200.39	$200.40	$200.40
Purchase #5	$118.87	6.832%	$126.9912	$126.99	$127.00	$127.00
Purchase #6	$226.94	10.324%	$250.3693	$250.37	$250.35	$250.40
Purchase #7	$180.65	4.690%	$189.1225	$189.12	$189.10	$189.10
7 purchase totals =	$1,081.35		$1,162.6217	$1,162.62	$1,162.60	$1,162.60