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	$105.74	5.438%	$111.4901	$111.49	$111.50	$111.50
Purchase #2	$92.97	8.678%	$101.0379	$101.04	$101.05	$101.00
Purchase #3	$96.97	13.204%	$109.7739	$109.77	$109.75	$109.80
Purchase #4	$46.30	9.694%	$50.7883	$50.79	$50.80	$50.80
Purchase #5	$76.62	8.867%	$83.4139	$83.41	$83.40	$83.40
Purchase #6	$168.99	3.275%	$174.5244	$174.52	$174.50	$174.50
Purchase #7	$46.93	5.596%	$49.5562	$49.56	$49.55	$49.60
7 purchase totals =	$634.52		$680.5847	$680.58	$680.55	$680.60