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	$87.43	13.757%	$99.4577	$99.46	$99.45	$99.50
Purchase #2	$36.49	7.623%	$39.2716	$39.27	$39.25	$39.30
Purchase #3	$54.98	13.125%	$62.1961	$62.20	$62.20	$62.20
Purchase #4	$87.91	13.693%	$99.9475	$99.95	$99.95	$99.90
Purchase #5	$101.48	4.745%	$106.2952	$106.30	$106.30	$106.30
Purchase #6	$138.74	10.409%	$153.1814	$153.18	$153.20	$153.20
Purchase #7	$16.31	10.565%	$18.0332	$18.03	$18.05	$18.00
7 purchase totals =	$523.34		$578.3827	$578.39	$578.40	$578.40