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	$180.32	13.289%	$204.2827	$204.28	$204.30	$204.30
Purchase #2	$120.97	10.617%	$133.8134	$133.81	$133.80	$133.80
Purchase #3	$62.48	4.129%	$65.0598	$65.06	$65.05	$65.10
Purchase #4	$96.64	4.208%	$100.7066	$100.71	$100.70	$100.70
Purchase #5	$72.77	8.160%	$78.708	$78.71	$78.70	$78.70
Purchase #6	$224.63	13.596%	$255.1707	$255.17	$255.15	$255.20
Purchase #7	$177.29	8.469%	$192.3047	$192.30	$192.30	$192.30
7 purchase totals =	$935.10		$1,030.0459	$1,030.04	$1,030.00	$1,030.10