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	$29.30	4.711%	$30.6803	$30.68	$30.70	$30.70
Purchase #2	$136.48	3.307%	$140.9934	$140.99	$141.00	$141.00
Purchase #3	$101.66	9.756%	$111.5779	$111.58	$111.60	$111.60
Purchase #4	$109.40	13.730%	$124.4206	$124.42	$124.40	$124.40
Purchase #5	$65.76	10.141%	$72.4287	$72.43	$72.45	$72.40
Purchase #6	$144.82	10.291%	$159.7234	$159.72	$159.70	$159.70
Purchase #7	$79.56	13.616%	$90.3929	$90.39	$90.40	$90.40
7 purchase totals =	$666.98		$730.2172	$730.21	$730.25	$730.20