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	$249.34	10.794%	$276.2538	$276.25	$276.25	$276.30
Purchase #2	$155.30	13.593%	$176.4099	$176.41	$176.40	$176.40
Purchase #3	$33.65	6.225%	$35.7447	$35.74	$35.75	$35.70
Purchase #4	$79.51	7.244%	$85.2697	$85.27	$85.25	$85.30
Purchase #5	$42.72	5.795%	$45.1956	$45.20	$45.20	$45.20
Purchase #6	$25.71	11.156%	$28.5782	$28.58	$28.60	$28.60
Purchase #7	$45.90	12.392%	$51.5879	$51.59	$51.60	$51.60
7 purchase totals =	$632.13		$699.0398	$699.04	$699.05	$699.10