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	$25.47	6.325%	$27.081	$27.08	$27.10	$27.10
Purchase #2	$37.76	8.117%	$40.825	$40.83	$40.85	$40.80
Purchase #3	$75.79	8.835%	$82.486	$82.49	$82.50	$82.50
Purchase #4	$194.87	11.519%	$217.3171	$217.32	$217.30	$217.30
Purchase #5	$101.86	7.852%	$109.858	$109.86	$109.85	$109.90
Purchase #6	$33.83	7.689%	$36.4312	$36.43	$36.45	$36.40
Purchase #7	$116.59	13.442%	$132.262	$132.26	$132.25	$132.30
7 purchase totals =	$586.17		$646.2603	$646.27	$646.30	$646.30