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	$47.34	8.420%	$51.326	$51.33	$51.35	$51.30
Purchase #2	$184.92	5.143%	$194.4304	$194.43	$194.45	$194.40
Purchase #3	$159.59	13.803%	$181.6182	$181.62	$181.60	$181.60
Purchase #4	$23.74	4.674%	$24.8496	$24.85	$24.85	$24.80
Purchase #5	$54.70	9.133%	$59.6958	$59.70	$59.70	$59.70
Purchase #6	$100.43	4.689%	$105.1392	$105.14	$105.15	$105.10
Purchase #7	$44.64	6.441%	$47.5153	$47.52	$47.50	$47.50
7 purchase totals =	$615.36		$664.5745	$664.59	$664.60	$664.40