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	$79.99	11.366%	$89.0817	$89.08	$89.10	$89.10
Purchase #2	$61.97	4.569%	$64.8014	$64.80	$64.80	$64.80
Purchase #3	$198.52	9.516%	$217.4112	$217.41	$217.40	$217.40
Purchase #4	$246.76	12.784%	$278.3058	$278.31	$278.30	$278.30
Purchase #5	$52.33	13.499%	$59.394	$59.39	$59.40	$59.40
Purchase #6	$92.60	7.215%	$99.2811	$99.28	$99.30	$99.30
Purchase #7	$29.96	10.747%	$33.1798	$33.18	$33.20	$33.20
7 purchase totals =	$762.13		$841.4550	$841.45	$841.50	$841.50