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	$16.51	3.237%	$17.0444	$17.04	$17.05	$17.00
Purchase #2	$39.80	13.810%	$45.2964	$45.30	$45.30	$45.30
Purchase #3	$235.39	8.716%	$255.9066	$255.91	$255.90	$255.90
Purchase #4	$117.66	8.440%	$127.5905	$127.59	$127.60	$127.60
Purchase #5	$228.50	11.499%	$254.7752	$254.78	$254.80	$254.80
Purchase #6	$29.88	6.270%	$31.7535	$31.75	$31.75	$31.80
Purchase #7	$214.69	13.510%	$243.6946	$243.69	$243.70	$243.70
7 purchase totals =	$882.43		$976.0612	$976.06	$976.10	$976.10