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	$43.67	3.733%	$45.3002	$45.30	$45.30	$45.30
Purchase #2	$185.26	6.256%	$196.8499	$196.85	$196.85	$196.80
Purchase #3	$185.27	4.743%	$194.0574	$194.06	$194.05	$194.10
Purchase #4	$80.60	3.117%	$83.1123	$83.11	$83.10	$83.10
Purchase #5	$200.91	5.598%	$212.1569	$212.16	$212.15	$212.20
Purchase #6	$166.84	11.748%	$186.4404	$186.44	$186.45	$186.40
Purchase #7	$35.52	9.574%	$38.9207	$38.92	$38.90	$38.90
7 purchase totals =	$898.07		$956.8378	$956.84	$956.80	$956.80