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	$179.76	11.356%	$200.1735	$200.17	$200.15	$200.20
Purchase #2	$111.83	6.781%	$119.4132	$119.41	$119.40	$119.40
Purchase #3	$81.31	9.683%	$89.1832	$89.18	$89.20	$89.20
Purchase #4	$43.93	3.842%	$45.6178	$45.62	$45.60	$45.60
Purchase #5	$158.32	4.371%	$165.2402	$165.24	$165.25	$165.20
Purchase #6	$25.89	10.351%	$28.5699	$28.57	$28.55	$28.60
Purchase #7	$134.84	8.857%	$146.7828	$146.78	$146.80	$146.80
7 purchase totals =	$735.88		$794.9806	$794.97	$794.95	$795.00