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	$134.61	6.244%	$143.015	$143.02	$143.00	$143.00
Purchase #2	$145.85	4.535%	$152.4643	$152.46	$152.45	$152.50
Purchase #3	$54.40	6.841%	$58.1215	$58.12	$58.10	$58.10
Purchase #4	$46.95	11.498%	$52.3483	$52.35	$52.35	$52.30
Purchase #5	$242.40	3.104%	$249.9241	$249.92	$249.90	$249.90
Purchase #6	$10.43	3.756%	$10.8218	$10.82	$10.80	$10.80
Purchase #7	$30.70	11.267%	$34.159	$34.16	$34.15	$34.20
7 purchase totals =	$665.34		$700.8540	$700.85	$700.75	$700.80