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	$90.46	10.678%	$100.1193	$100.12	$100.10	$100.10
Purchase #2	$204.77	7.671%	$220.4779	$220.48	$220.50	$220.50
Purchase #3	$54.29	8.697%	$59.0116	$59.01	$59.00	$59.00
Purchase #4	$24.84	9.868%	$27.2912	$27.29	$27.30	$27.30
Purchase #5	$189.67	8.847%	$206.4501	$206.45	$206.45	$206.50
Purchase #6	$149.65	10.706%	$165.6715	$165.67	$165.65	$165.70
Purchase #7	$232.75	10.167%	$256.4137	$256.41	$256.40	$256.40
7 purchase totals =	$946.43		$1,035.4353	$1,035.43	$1,035.40	$1,035.50