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	$57.31	3.202%	$59.1451	$59.15	$59.15	$59.10
Purchase #2	$32.58	4.213%	$33.9526	$33.95	$33.95	$34.00
Purchase #3	$129.27	12.465%	$145.3835	$145.38	$145.40	$145.40
Purchase #4	$38.40	6.433%	$40.8703	$40.87	$40.85	$40.90
Purchase #5	$241.49	5.466%	$254.6898	$254.69	$254.70	$254.70
Purchase #6	$59.45	5.862%	$62.935	$62.94	$62.95	$62.90
Purchase #7	$37.66	9.549%	$41.2562	$41.26	$41.25	$41.30
7 purchase totals =	$596.16		$638.2325	$638.24	$638.25	$638.30