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	$7.30	10.421%	$8.0607	$8.06	$8.05	$8.10
Purchase #2	$161.66	7.252%	$173.3836	$173.38	$173.40	$173.40
Purchase #3	$188.80	12.142%	$211.7241	$211.72	$211.70	$211.70
Purchase #4	$38.38	10.662%	$42.4721	$42.47	$42.45	$42.50
Purchase #5	$41.93	10.440%	$46.3075	$46.31	$46.30	$46.30
Purchase #6	$48.54	11.598%	$54.1697	$54.17	$54.15	$54.20
Purchase #7	$134.66	7.579%	$144.8659	$144.87	$144.85	$144.90
7 purchase totals =	$621.27		$680.9836	$680.98	$680.90	$681.10