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	$144.72	3.784%	$150.1962	$150.20	$150.20	$150.20
Purchase #2	$150.65	11.388%	$167.806	$167.81	$167.80	$167.80
Purchase #3	$208.76	7.415%	$224.2396	$224.24	$224.25	$224.20
Purchase #4	$62.33	9.696%	$68.3735	$68.37	$68.35	$68.40
Purchase #5	$221.38	3.138%	$228.3269	$228.33	$228.35	$228.30
Purchase #6	$155.50	11.640%	$173.6002	$173.60	$173.60	$173.60
Purchase #7	$77.47	13.531%	$87.9525	$87.95	$87.95	$88.00
7 purchase totals =	$1,020.81		$1,100.4949	$1,100.50	$1,100.50	$1,100.50