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	$51.92	13.752%	$59.06	$59.06	$59.05	$59.10
Purchase #2	$43.72	11.662%	$48.8186	$48.82	$48.80	$48.80
Purchase #3	$77.39	4.677%	$81.0095	$81.01	$81.00	$81.00
Purchase #4	$123.59	7.168%	$132.4489	$132.45	$132.45	$132.40
Purchase #5	$37.38	5.343%	$39.3772	$39.38	$39.40	$39.40
Purchase #6	$51.51	10.735%	$57.0396	$57.04	$57.05	$57.00
Purchase #7	$166.60	10.870%	$184.7094	$184.71	$184.70	$184.70
7 purchase totals =	$552.11		$602.4632	$602.47	$602.45	$602.40