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	$20.53	8.537%	$22.2826	$22.28	$22.30	$22.30
Purchase #2	$153.60	4.773%	$160.9313	$160.93	$160.95	$160.90
Purchase #3	$111.85	10.713%	$123.8325	$123.83	$123.85	$123.80
Purchase #4	$61.38	9.414%	$67.1583	$67.16	$67.15	$67.20
Purchase #5	$152.58	9.308%	$166.7821	$166.78	$166.80	$166.80
Purchase #6	$224.27	11.311%	$249.6372	$249.64	$249.65	$249.60
Purchase #7	$132.77	11.426%	$147.9403	$147.94	$147.95	$147.90
7 purchase totals =	$856.98		$938.5643	$938.56	$938.65	$938.50