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	$225.97	10.732%	$250.2211	$250.22	$250.20	$250.20
Purchase #2	$148.52	10.785%	$164.5379	$164.54	$164.55	$164.50
Purchase #3	$56.43	7.362%	$60.5844	$60.58	$60.60	$60.60
Purchase #4	$205.37	11.287%	$228.5501	$228.55	$228.55	$228.60
Purchase #5	$147.28	5.526%	$155.4187	$155.42	$155.40	$155.40
Purchase #6	$112.45	5.412%	$118.5358	$118.54	$118.55	$118.50
Purchase #7	$143.92	10.666%	$159.2705	$159.27	$159.25	$159.30
7 purchase totals =	$1,039.94		$1,137.1185	$1,137.12	$1,137.10	$1,137.10