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	$57.64	7.130%	$61.7497	$61.75	$61.75	$61.70
Purchase #2	$48.59	12.381%	$54.6059	$54.61	$54.60	$54.60
Purchase #3	$48.88	11.673%	$54.5858	$54.59	$54.60	$54.60
Purchase #4	$103.93	9.555%	$113.8605	$113.86	$113.85	$113.90
Purchase #5	$125.35	6.325%	$133.2784	$133.28	$133.30	$133.30
Purchase #6	$63.81	10.252%	$70.3518	$70.35	$70.35	$70.40
Purchase #7	$154.54	10.689%	$171.0588	$171.06	$171.05	$171.10
7 purchase totals =	$602.74		$659.4909	$659.50	$659.50	$659.60