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	$5.49	3.679%	$5.692	$5.69	$5.70	$5.70
Purchase #2	$169.42	7.699%	$182.4636	$182.46	$182.45	$182.50
Purchase #3	$111.56	5.292%	$117.4638	$117.46	$117.45	$117.50
Purchase #4	$24.64	12.649%	$27.7567	$27.76	$27.75	$27.80
Purchase #5	$249.33	13.452%	$282.8699	$282.87	$282.85	$282.90
Purchase #6	$20.52	5.229%	$21.593	$21.59	$21.60	$21.60
Purchase #7	$60.89	7.718%	$65.5895	$65.59	$65.60	$65.60
7 purchase totals =	$641.85		$703.4285	$703.42	$703.40	$703.60