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	$199.35	8.286%	$215.8681	$215.87	$215.85	$215.90
Purchase #2	$246.50	13.247%	$279.1539	$279.15	$279.15	$279.20
Purchase #3	$91.97	9.486%	$100.6943	$100.69	$100.70	$100.70
Purchase #4	$65.72	7.282%	$70.5057	$70.51	$70.50	$70.50
Purchase #5	$153.36	9.789%	$168.3724	$168.37	$168.35	$168.40
Purchase #6	$48.28	11.505%	$53.8346	$53.83	$53.85	$53.80
Purchase #7	$25.41	5.866%	$26.9006	$26.90	$26.90	$26.90
7 purchase totals =	$830.59		$915.3296	$915.32	$915.30	$915.40