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	$76.72	8.325%	$83.1069	$83.11	$83.10	$83.10
Purchase #2	$189.98	10.262%	$209.4757	$209.48	$209.50	$209.50
Purchase #3	$57.63	13.265%	$65.2746	$65.27	$65.25	$65.30
Purchase #4	$49.85	7.224%	$53.4512	$53.45	$53.45	$53.50
Purchase #5	$162.37	8.516%	$176.1974	$176.20	$176.20	$176.20
Purchase #6	$10.96	12.389%	$12.3178	$12.32	$12.30	$12.30
Purchase #7	$162.99	9.503%	$178.4789	$178.48	$178.50	$178.50
7 purchase totals =	$710.50		$778.3025	$778.31	$778.30	$778.40