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	$92.77	8.745%	$100.8827	$100.88	$100.90	$100.90
Purchase #2	$45.64	8.483%	$49.5116	$49.51	$49.50	$49.50
Purchase #3	$24.69	13.317%	$27.978	$27.98	$28.00	$28.00
Purchase #4	$36.44	12.200%	$40.8857	$40.89	$40.90	$40.90
Purchase #5	$16.43	6.145%	$17.4396	$17.44	$17.45	$17.40
Purchase #6	$224.97	5.534%	$237.4198	$237.42	$237.40	$237.40
Purchase #7	$94.61	5.291%	$99.6158	$99.62	$99.60	$99.60
7 purchase totals =	$535.55		$573.7332	$573.74	$573.75	$573.70