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	$161.88	13.262%	$183.3485	$183.35	$183.35	$183.30
Purchase #2	$178.73	9.760%	$196.174	$196.17	$196.15	$196.20
Purchase #3	$33.88	12.563%	$38.1363	$38.14	$38.15	$38.10
Purchase #4	$139.78	8.789%	$152.0653	$152.07	$152.05	$152.10
Purchase #5	$214.47	6.261%	$227.898	$227.90	$227.90	$227.90
Purchase #6	$101.37	8.746%	$110.2358	$110.24	$110.25	$110.20
Purchase #7	$138.88	10.602%	$153.6041	$153.60	$153.60	$153.60
7 purchase totals =	$968.99		$1,061.4620	$1,061.47	$1,061.45	$1,061.40