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	$13.32	12.486%	$14.9831	$14.98	$15.00	$15.00
Purchase #2	$97.78	12.641%	$110.1404	$110.14	$110.15	$110.10
Purchase #3	$80.53	12.319%	$90.4505	$90.45	$90.45	$90.50
Purchase #4	$92.84	12.341%	$104.2974	$104.30	$104.30	$104.30
Purchase #5	$184.75	5.527%	$194.9611	$194.96	$194.95	$195.00
Purchase #6	$38.58	4.408%	$40.2806	$40.28	$40.30	$40.30
Purchase #7	$56.75	5.535%	$59.8911	$59.89	$59.90	$59.90
7 purchase totals =	$564.55		$615.0042	$615.00	$615.05	$615.10