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	$140.54	13.113%	$158.969	$158.97	$158.95	$159.00
Purchase #2	$174.83	7.704%	$188.2989	$188.30	$188.30	$188.30
Purchase #3	$224.75	11.781%	$251.2278	$251.23	$251.25	$251.20
Purchase #4	$115.48	12.869%	$130.3411	$130.34	$130.35	$130.30
Purchase #5	$10.45	5.603%	$11.0355	$11.04	$11.05	$11.00
Purchase #6	$84.47	7.443%	$90.7571	$90.76	$90.75	$90.80
Purchase #7	$226.88	13.106%	$256.6149	$256.61	$256.60	$256.60
7 purchase totals =	$977.40		$1,087.2443	$1,087.25	$1,087.25	$1,087.20