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	$233.29	7.584%	$250.9827	$250.98	$251.00	$251.00
Purchase #2	$91.27	4.805%	$95.6555	$95.66	$95.65	$95.70
Purchase #3	$19.40	7.178%	$20.7925	$20.79	$20.80	$20.80
Purchase #4	$99.57	6.307%	$105.8499	$105.85	$105.85	$105.80
Purchase #5	$153.31	11.343%	$170.7	$170.70	$170.70	$170.70
Purchase #6	$100.54	4.516%	$105.0804	$105.08	$105.10	$105.10
Purchase #7	$48.75	8.270%	$52.7816	$52.78	$52.80	$52.80
7 purchase totals =	$746.13		$801.8426	$801.84	$801.90	$801.90