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	$35.41	12.743%	$39.9223	$39.92	$39.90	$39.90
Purchase #2	$220.60	10.105%	$242.8916	$242.89	$242.90	$242.90
Purchase #3	$54.92	8.826%	$59.7672	$59.77	$59.75	$59.80
Purchase #4	$224.35	9.485%	$245.6296	$245.63	$245.65	$245.60
Purchase #5	$158.76	13.659%	$180.445	$180.45	$180.45	$180.40
Purchase #6	$162.38	6.510%	$172.9509	$172.95	$172.95	$173.00
Purchase #7	$122.36	5.174%	$128.6909	$128.69	$128.70	$128.70
7 purchase totals =	$978.78		$1,070.2975	$1,070.30	$1,070.30	$1,070.30