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	$19.36	9.810%	$21.2592	$21.26	$21.25	$21.30
Purchase #2	$43.85	3.672%	$45.4602	$45.46	$45.45	$45.50
Purchase #3	$39.74	6.373%	$42.2726	$42.27	$42.25	$42.30
Purchase #4	$107.73	3.631%	$111.6417	$111.64	$111.65	$111.60
Purchase #5	$186.61	12.136%	$209.257	$209.26	$209.25	$209.30
Purchase #6	$109.67	6.310%	$116.5902	$116.59	$116.60	$116.60
Purchase #7	$151.98	10.757%	$168.3285	$168.33	$168.35	$168.30
7 purchase totals =	$658.94		$714.8094	$714.81	$714.80	$714.90