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	$30.52	12.215%	$34.248	$34.25	$34.25	$34.20
Purchase #2	$184.86	11.755%	$206.5903	$206.59	$206.60	$206.60
Purchase #3	$92.95	8.747%	$101.0803	$101.08	$101.10	$101.10
Purchase #4	$157.28	5.368%	$165.7228	$165.72	$165.70	$165.70
Purchase #5	$128.42	11.673%	$143.4105	$143.41	$143.40	$143.40
Purchase #6	$52.54	13.226%	$59.4889	$59.49	$59.50	$59.50
Purchase #7	$65.91	5.531%	$69.5555	$69.56	$69.55	$69.60
7 purchase totals =	$712.48		$780.0963	$780.10	$780.10	$780.10