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	$92.65	7.127%	$99.2532	$99.25	$99.25	$99.30
Purchase #2	$102.94	7.850%	$111.0208	$111.02	$111.00	$111.00
Purchase #3	$173.92	11.643%	$194.1695	$194.17	$194.15	$194.20
Purchase #4	$119.89	10.680%	$132.6943	$132.69	$132.70	$132.70
Purchase #5	$151.37	7.583%	$162.8484	$162.85	$162.85	$162.80
Purchase #6	$247.75	3.436%	$256.2627	$256.26	$256.25	$256.30
Purchase #7	$88.45	11.839%	$98.9216	$98.92	$98.90	$98.90
7 purchase totals =	$976.97		$1,055.1705	$1,055.16	$1,055.10	$1,055.20