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	$249.28	11.667%	$278.3635	$278.36	$278.35	$278.40
Purchase #2	$16.72	11.793%	$18.6918	$18.69	$18.70	$18.70
Purchase #3	$62.30	6.415%	$66.2965	$66.30	$66.30	$66.30
Purchase #4	$40.82	8.318%	$44.2154	$44.22	$44.20	$44.20
Purchase #5	$83.47	11.196%	$92.8153	$92.82	$92.80	$92.80
Purchase #6	$52.85	5.343%	$55.6738	$55.67	$55.65	$55.70
Purchase #7	$42.61	7.563%	$45.8326	$45.83	$45.85	$45.80
7 purchase totals =	$548.05		$601.8889	$601.89	$601.85	$601.90