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	$24.93	12.733%	$28.1043	$28.10	$28.10	$28.10
Purchase #2	$36.93	9.614%	$40.4805	$40.48	$40.50	$40.50
Purchase #3	$143.87	4.123%	$149.8018	$149.80	$149.80	$149.80
Purchase #4	$124.51	8.290%	$134.8319	$134.83	$134.85	$134.80
Purchase #5	$220.84	5.577%	$233.1562	$233.16	$233.15	$233.20
Purchase #6	$37.63	3.360%	$38.8944	$38.89	$38.90	$38.90
Purchase #7	$80.60	5.820%	$85.2909	$85.29	$85.30	$85.30
7 purchase totals =	$669.31		$710.5600	$710.55	$710.60	$710.60