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	$27.93	6.151%	$29.648	$29.65	$29.65	$29.60
Purchase #2	$146.94	5.472%	$154.9806	$154.98	$155.00	$155.00
Purchase #3	$68.51	7.761%	$73.8271	$73.83	$73.85	$73.80
Purchase #4	$129.40	6.587%	$137.9236	$137.92	$137.90	$137.90
Purchase #5	$32.63	11.459%	$36.3691	$36.37	$36.35	$36.40
Purchase #6	$116.72	9.196%	$127.4536	$127.45	$127.45	$127.50
Purchase #7	$64.54	9.398%	$70.6055	$70.61	$70.60	$70.60
7 purchase totals =	$586.67		$630.8075	$630.81	$630.80	$630.80