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	$34.54	11.411%	$38.4814	$38.48	$38.50	$38.50
Purchase #2	$132.54	4.332%	$138.2816	$138.28	$138.30	$138.30
Purchase #3	$134.52	13.360%	$152.4919	$152.49	$152.50	$152.50
Purchase #4	$127.87	4.771%	$133.9707	$133.97	$133.95	$134.00
Purchase #5	$149.86	9.551%	$164.1731	$164.17	$164.15	$164.20
Purchase #6	$241.69	11.631%	$269.801	$269.80	$269.80	$269.80
Purchase #7	$226.49	8.243%	$245.1596	$245.16	$245.15	$245.20
7 purchase totals =	$1,047.51		$1,142.3593	$1,142.35	$1,142.35	$1,142.50