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	$224.63	11.508%	$250.4804	$250.48	$250.50	$250.50
Purchase #2	$146.29	13.644%	$166.2498	$166.25	$166.25	$166.20
Purchase #3	$88.65	13.801%	$100.8846	$100.88	$100.90	$100.90
Purchase #4	$14.28	7.707%	$15.3806	$15.38	$15.40	$15.40
Purchase #5	$193.95	8.286%	$210.0207	$210.02	$210.00	$210.00
Purchase #6	$47.83	8.243%	$51.7726	$51.77	$51.75	$51.80
Purchase #7	$104.94	10.800%	$116.2735	$116.27	$116.25	$116.30
7 purchase totals =	$820.57		$911.0622	$911.05	$911.05	$911.10