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	$103.48	7.624%	$111.3693	$111.37	$111.35	$111.40
Purchase #2	$158.34	8.190%	$171.308	$171.31	$171.30	$171.30
Purchase #3	$44.84	4.333%	$46.7829	$46.78	$46.80	$46.80
Purchase #4	$84.45	6.781%	$90.1766	$90.18	$90.20	$90.20
Purchase #5	$60.63	10.570%	$67.0386	$67.04	$67.05	$67.00
Purchase #6	$136.52	12.870%	$154.0901	$154.09	$154.10	$154.10
Purchase #7	$70.78	11.676%	$79.0443	$79.04	$79.05	$79.00
7 purchase totals =	$659.04		$719.8098	$719.81	$719.85	$719.80