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	$105.73	12.471%	$118.9156	$118.92	$118.90	$118.90
Purchase #2	$238.52	10.776%	$264.2229	$264.22	$264.20	$264.20
Purchase #3	$118.51	12.141%	$132.8983	$132.90	$132.90	$132.90
Purchase #4	$41.82	5.604%	$44.1636	$44.16	$44.15	$44.20
Purchase #5	$55.49	9.565%	$60.7976	$60.80	$60.80	$60.80
Purchase #6	$175.35	5.769%	$185.4659	$185.47	$185.45	$185.50
Purchase #7	$113.61	11.570%	$126.7547	$126.75	$126.75	$126.80
7 purchase totals =	$849.03		$933.2186	$933.22	$933.15	$933.30