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	$30.44	4.462%	$31.7982	$31.80	$31.80	$31.80
Purchase #2	$78.84	13.753%	$89.6829	$89.68	$89.70	$89.70
Purchase #3	$97.77	13.788%	$111.2505	$111.25	$111.25	$111.30
Purchase #4	$66.48	13.756%	$75.625	$75.63	$75.65	$75.60
Purchase #5	$103.45	13.529%	$117.4458	$117.45	$117.45	$117.40
Purchase #6	$54.64	6.455%	$58.167	$58.17	$58.15	$58.20
Purchase #7	$127.85	3.544%	$132.381	$132.38	$132.40	$132.40
7 purchase totals =	$559.47		$616.3504	$616.36	$616.40	$616.40