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	$74.70	5.224%	$78.6023	$78.60	$78.60	$78.60
Purchase #2	$80.58	12.493%	$90.6469	$90.65	$90.65	$90.60
Purchase #3	$232.52	13.303%	$263.4521	$263.45	$263.45	$263.50
Purchase #4	$128.83	12.820%	$145.346	$145.35	$145.35	$145.30
Purchase #5	$166.82	9.727%	$183.0466	$183.05	$183.05	$183.00
Purchase #6	$82.40	8.427%	$89.3438	$89.34	$89.35	$89.30
Purchase #7	$65.71	9.660%	$72.0576	$72.06	$72.05	$72.10
7 purchase totals =	$831.56		$922.4953	$922.50	$922.50	$922.40