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	$91.33	9.431%	$99.9433	$99.94	$99.95	$99.90
Purchase #2	$56.97	9.613%	$62.4465	$62.45	$62.45	$62.40
Purchase #3	$116.72	5.364%	$122.9809	$122.98	$123.00	$123.00
Purchase #4	$74.27	3.404%	$76.7982	$76.80	$76.80	$76.80
Purchase #5	$128.36	4.611%	$134.2787	$134.28	$134.30	$134.30
Purchase #6	$173.67	4.118%	$180.8217	$180.82	$180.80	$180.80
Purchase #7	$37.49	10.233%	$41.3264	$41.33	$41.35	$41.30
7 purchase totals =	$678.81		$718.5957	$718.60	$718.65	$718.50