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	$229.45	5.728%	$242.5929	$242.59	$242.60	$242.60
Purchase #2	$41.92	8.496%	$45.4815	$45.48	$45.50	$45.50
Purchase #3	$100.73	13.333%	$114.1603	$114.16	$114.15	$114.20
Purchase #4	$12.42	11.351%	$13.8298	$13.83	$13.85	$13.80
Purchase #5	$135.51	6.842%	$144.7816	$144.78	$144.80	$144.80
Purchase #6	$235.99	3.389%	$243.9877	$243.99	$244.00	$244.00
Purchase #7	$32.81	13.667%	$37.2941	$37.29	$37.30	$37.30
7 purchase totals =	$788.83		$842.1279	$842.12	$842.20	$842.20