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	$231.67	10.207%	$255.3166	$255.32	$255.30	$255.30
Purchase #2	$146.64	5.627%	$154.8914	$154.89	$154.90	$154.90
Purchase #3	$78.70	9.670%	$86.3103	$86.31	$86.30	$86.30
Purchase #4	$32.96	7.454%	$35.4168	$35.42	$35.40	$35.40
Purchase #5	$228.91	5.103%	$240.5913	$240.59	$240.60	$240.60
Purchase #6	$97.72	12.155%	$109.5979	$109.60	$109.60	$109.60
Purchase #7	$15.35	12.261%	$17.2321	$17.23	$17.25	$17.20
7 purchase totals =	$831.95		$899.3564	$899.36	$899.35	$899.30