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	$230.87	4.173%	$240.5042	$240.50	$240.50	$240.50
Purchase #2	$221.32	8.637%	$240.4354	$240.44	$240.45	$240.40
Purchase #3	$85.32	11.180%	$94.8588	$94.86	$94.85	$94.90
Purchase #4	$238.69	9.841%	$262.1795	$262.18	$262.20	$262.20
Purchase #5	$210.60	7.321%	$226.018	$226.02	$226.00	$226.00
Purchase #6	$59.25	10.168%	$65.2745	$65.27	$65.25	$65.30
Purchase #7	$63.73	4.801%	$66.7897	$66.79	$66.80	$66.80
7 purchase totals =	$1,109.78		$1,196.0601	$1,196.06	$1,196.05	$1,196.10