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	$205.90	5.866%	$217.9781	$217.98	$218.00	$218.00
Purchase #2	$108.62	11.168%	$120.7507	$120.75	$120.75	$120.80
Purchase #3	$61.96	4.226%	$64.5784	$64.58	$64.60	$64.60
Purchase #4	$100.68	10.528%	$111.2796	$111.28	$111.30	$111.30
Purchase #5	$138.25	4.723%	$144.7795	$144.78	$144.80	$144.80
Purchase #6	$92.91	5.687%	$98.1938	$98.19	$98.20	$98.20
Purchase #7	$156.37	7.177%	$167.5927	$167.59	$167.60	$167.60
7 purchase totals =	$864.69		$925.1528	$925.15	$925.25	$925.30