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	$242.83	13.424%	$275.4275	$275.43	$275.45	$275.40
Purchase #2	$52.83	13.374%	$59.8955	$59.90	$59.90	$59.90
Purchase #3	$130.46	6.758%	$139.2765	$139.28	$139.30	$139.30
Purchase #4	$215.51	3.237%	$222.4861	$222.49	$222.50	$222.50
Purchase #5	$134.87	13.549%	$153.1435	$153.14	$153.15	$153.10
Purchase #6	$24.34	13.216%	$27.5568	$27.56	$27.55	$27.60
Purchase #7	$212.55	8.319%	$230.232	$230.23	$230.25	$230.20
7 purchase totals =	$1,013.39		$1,108.0179	$1,108.03	$1,108.10	$1,108.00