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	$5.81	11.417%	$6.4733	$6.47	$6.45	$6.50
Purchase #2	$220.32	9.422%	$241.0786	$241.08	$241.10	$241.10
Purchase #3	$18.28	8.497%	$19.8333	$19.83	$19.85	$19.80
Purchase #4	$113.81	3.718%	$118.0415	$118.04	$118.05	$118.00
Purchase #5	$236.52	11.764%	$264.3442	$264.34	$264.35	$264.30
Purchase #6	$165.58	3.460%	$171.3091	$171.31	$171.30	$171.30
Purchase #7	$41.50	8.865%	$45.179	$45.18	$45.20	$45.20
7 purchase totals =	$801.82		$866.2590	$866.25	$866.30	$866.20