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	$117.90	12.231%	$132.3203	$132.32	$132.30	$132.30
Purchase #2	$18.59	7.501%	$19.9844	$19.98	$20.00	$20.00
Purchase #3	$77.59	9.741%	$85.148	$85.15	$85.15	$85.10
Purchase #4	$82.25	12.449%	$92.4893	$92.49	$92.50	$92.50
Purchase #5	$188.47	10.795%	$208.8153	$208.82	$208.80	$208.80
Purchase #6	$72.75	11.446%	$81.077	$81.08	$81.10	$81.10
Purchase #7	$82.62	9.665%	$90.6052	$90.61	$90.60	$90.60
7 purchase totals =	$640.17		$710.4395	$710.45	$710.45	$710.40