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	$15.89	7.258%	$17.0433	$17.04	$17.05	$17.00
Purchase #2	$56.59	10.432%	$62.4935	$62.49	$62.50	$62.50
Purchase #3	$142.27	13.332%	$161.2374	$161.24	$161.25	$161.20
Purchase #4	$122.83	3.826%	$127.5295	$127.53	$127.55	$127.50
Purchase #5	$81.62	10.119%	$89.8791	$89.88	$89.90	$89.90
Purchase #6	$104.96	12.200%	$117.7651	$117.77	$117.75	$117.80
Purchase #7	$47.92	6.731%	$51.1455	$51.15	$51.15	$51.10
7 purchase totals =	$572.08		$627.0934	$627.10	$627.15	$627.00