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	$30.97	11.368%	$34.4907	$34.49	$34.50	$34.50
Purchase #2	$185.69	10.621%	$205.4121	$205.41	$205.40	$205.40
Purchase #3	$199.39	8.490%	$216.3182	$216.32	$216.30	$216.30
Purchase #4	$143.40	10.190%	$158.0125	$158.01	$158.00	$158.00
Purchase #5	$37.58	9.476%	$41.1411	$41.14	$41.15	$41.10
Purchase #6	$83.53	6.433%	$88.9035	$88.90	$88.90	$88.90
Purchase #7	$17.82	12.212%	$19.9962	$20.00	$20.00	$20.00
7 purchase totals =	$698.38		$764.2743	$764.27	$764.25	$764.20