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	$39.69	5.267%	$41.7805	$41.78	$41.80	$41.80
Purchase #2	$213.57	9.217%	$233.2547	$233.25	$233.25	$233.30
Purchase #3	$82.74	8.376%	$89.6703	$89.67	$89.65	$89.70
Purchase #4	$149.78	8.335%	$162.2642	$162.26	$162.25	$162.30
Purchase #5	$155.82	7.430%	$167.3974	$167.40	$167.40	$167.40
Purchase #6	$22.78	12.448%	$25.6157	$25.62	$25.60	$25.60
Purchase #7	$71.57	13.262%	$81.0616	$81.06	$81.05	$81.10
7 purchase totals =	$735.95		$801.0444	$801.04	$801.00	$801.20