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	$114.47	12.181%	$128.4136	$128.41	$128.40	$128.40
Purchase #2	$169.44	3.784%	$175.8516	$175.85	$175.85	$175.90
Purchase #3	$29.93	6.387%	$31.8416	$31.84	$31.85	$31.80
Purchase #4	$9.66	6.797%	$10.3166	$10.32	$10.30	$10.30
Purchase #5	$54.47	13.104%	$61.6077	$61.61	$61.60	$61.60
Purchase #6	$228.31	11.306%	$254.1227	$254.12	$254.10	$254.10
Purchase #7	$176.98	4.229%	$184.4645	$184.46	$184.45	$184.50
7 purchase totals =	$783.26		$846.6183	$846.61	$846.55	$846.60