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	$143.34	13.828%	$163.1611	$163.16	$163.15	$163.20
Purchase #2	$75.86	10.389%	$83.7411	$83.74	$83.75	$83.70
Purchase #3	$231.81	13.300%	$262.6407	$262.64	$262.65	$262.60
Purchase #4	$184.32	6.838%	$196.9238	$196.92	$196.90	$196.90
Purchase #5	$53.87	3.565%	$55.7905	$55.79	$55.80	$55.80
Purchase #6	$87.86	12.747%	$99.0595	$99.06	$99.05	$99.10
Purchase #7	$51.51	10.772%	$57.0587	$57.06	$57.05	$57.10
7 purchase totals =	$828.57		$918.3754	$918.37	$918.35	$918.40