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	$87.27	13.793%	$99.3072	$99.31	$99.30	$99.30
Purchase #2	$34.44	11.457%	$38.3858	$38.39	$38.40	$38.40
Purchase #3	$93.45	12.372%	$105.0116	$105.01	$105.00	$105.00
Purchase #4	$45.91	7.398%	$49.3064	$49.31	$49.30	$49.30
Purchase #5	$156.68	12.422%	$176.1428	$176.14	$176.15	$176.10
Purchase #6	$237.53	5.614%	$250.8649	$250.86	$250.85	$250.90
Purchase #7	$173.82	4.786%	$182.139	$182.14	$182.15	$182.10
7 purchase totals =	$829.10		$901.1577	$901.16	$901.15	$901.10