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	$89.64	10.616%	$99.1562	$99.16	$99.15	$99.20
Purchase #2	$204.32	5.855%	$216.2829	$216.28	$216.30	$216.30
Purchase #3	$247.36	5.186%	$260.1881	$260.19	$260.20	$260.20
Purchase #4	$196.77	7.162%	$210.8627	$210.86	$210.85	$210.90
Purchase #5	$241.84	6.720%	$258.0916	$258.09	$258.10	$258.10
Purchase #6	$82.79	11.294%	$92.1403	$92.14	$92.15	$92.10
Purchase #7	$67.91	7.291%	$72.8613	$72.86	$72.85	$72.90
7 purchase totals =	$1,130.63		$1,209.5831	$1,209.58	$1,209.60	$1,209.70