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	$151.59	10.732%	$167.8586	$167.86	$167.85	$167.90
Purchase #2	$220.90	8.824%	$240.3922	$240.39	$240.40	$240.40
Purchase #3	$178.47	5.179%	$187.713	$187.71	$187.70	$187.70
Purchase #4	$116.58	11.132%	$129.5577	$129.56	$129.55	$129.60
Purchase #5	$111.58	4.428%	$116.5208	$116.52	$116.50	$116.50
Purchase #6	$31.64	8.304%	$34.2674	$34.27	$34.25	$34.30
Purchase #7	$57.25	11.763%	$63.9843	$63.98	$64.00	$64.00
7 purchase totals =	$868.01		$940.2940	$940.29	$940.25	$940.40