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	$221.41	8.148%	$239.4505	$239.45	$239.45	$239.50
Purchase #2	$199.81	10.264%	$220.3185	$220.32	$220.30	$220.30
Purchase #3	$89.30	11.536%	$99.6016	$99.60	$99.60	$99.60
Purchase #4	$52.33	12.461%	$58.8508	$58.85	$58.85	$58.90
Purchase #5	$222.68	8.152%	$240.8329	$240.83	$240.85	$240.80
Purchase #6	$181.83	10.198%	$200.373	$200.37	$200.35	$200.40
Purchase #7	$34.34	10.113%	$37.8128	$37.81	$37.80	$37.80
7 purchase totals =	$1,001.70		$1,097.2401	$1,097.23	$1,097.20	$1,097.30