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	$10.56	13.292%	$11.9636	$11.96	$11.95	$12.00
Purchase #2	$77.39	6.167%	$82.1626	$82.16	$82.15	$82.20
Purchase #3	$196.64	9.202%	$214.7348	$214.73	$214.75	$214.70
Purchase #4	$87.78	8.654%	$95.3765	$95.38	$95.40	$95.40
Purchase #5	$51.63	12.628%	$58.1498	$58.15	$58.15	$58.10
Purchase #6	$148.95	4.395%	$155.4964	$155.50	$155.50	$155.50
Purchase #7	$44.50	11.505%	$49.6197	$49.62	$49.60	$49.60
7 purchase totals =	$617.45		$667.5034	$667.50	$667.50	$667.50