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	$123.29	4.300%	$128.5915	$128.59	$128.60	$128.60
Purchase #2	$52.34	3.460%	$54.151	$54.15	$54.15	$54.20
Purchase #3	$53.59	10.497%	$59.2153	$59.22	$59.20	$59.20
Purchase #4	$9.36	9.176%	$10.2189	$10.22	$10.20	$10.20
Purchase #5	$216.56	5.337%	$228.1178	$228.12	$228.10	$228.10
Purchase #6	$116.77	11.836%	$130.5909	$130.59	$130.60	$130.60
Purchase #7	$211.66	8.779%	$230.2416	$230.24	$230.25	$230.20
7 purchase totals =	$783.57		$841.1270	$841.13	$841.10	$841.10