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	$19.90	4.685%	$20.8323	$20.83	$20.85	$20.80
Purchase #2	$16.77	11.657%	$18.7249	$18.72	$18.70	$18.70
Purchase #3	$174.81	12.239%	$196.205	$196.21	$196.20	$196.20
Purchase #4	$95.63	6.263%	$101.6193	$101.62	$101.60	$101.60
Purchase #5	$228.92	5.477%	$241.4579	$241.46	$241.45	$241.50
Purchase #6	$125.41	11.476%	$139.8021	$139.80	$139.80	$139.80
Purchase #7	$177.63	7.517%	$190.9824	$190.98	$191.00	$191.00
7 purchase totals =	$839.07		$909.6239	$909.62	$909.60	$909.60