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	$50.29	8.287%	$54.4575	$54.46	$54.45	$54.50
Purchase #2	$61.92	7.216%	$66.3881	$66.39	$66.40	$66.40
Purchase #3	$16.31	13.774%	$18.5565	$18.56	$18.55	$18.60
Purchase #4	$169.32	9.729%	$185.7931	$185.79	$185.80	$185.80
Purchase #5	$208.83	5.766%	$220.8711	$220.87	$220.85	$220.90
Purchase #6	$11.29	6.274%	$11.9983	$12.00	$12.00	$12.00
Purchase #7	$199.98	12.414%	$224.8055	$224.81	$224.80	$224.80
7 purchase totals =	$717.94		$782.8701	$782.88	$782.85	$783.00