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	$250.74	6.620%	$267.339	$267.34	$267.35	$267.30
Purchase #2	$189.98	11.492%	$211.8125	$211.81	$211.80	$211.80
Purchase #3	$113.52	4.323%	$118.4275	$118.43	$118.45	$118.40
Purchase #4	$45.76	5.605%	$48.3248	$48.32	$48.30	$48.30
Purchase #5	$176.56	8.657%	$191.8448	$191.84	$191.85	$191.80
Purchase #6	$100.50	3.407%	$103.924	$103.92	$103.90	$103.90
Purchase #7	$192.49	11.727%	$215.0633	$215.06	$215.05	$215.10
7 purchase totals =	$1,069.55		$1,156.7359	$1,156.72	$1,156.70	$1,156.60