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	$37.67	5.689%	$39.813	$39.81	$39.80	$39.80
Purchase #2	$44.72	3.286%	$46.1895	$46.19	$46.20	$46.20
Purchase #3	$139.32	5.200%	$146.5646	$146.56	$146.55	$146.60
Purchase #4	$66.64	6.286%	$70.829	$70.83	$70.85	$70.80
Purchase #5	$82.79	8.583%	$89.8959	$89.90	$89.90	$89.90
Purchase #6	$206.75	8.634%	$224.6008	$224.60	$224.60	$224.60
Purchase #7	$206.68	5.162%	$217.3488	$217.35	$217.35	$217.30
7 purchase totals =	$784.57		$835.2416	$835.24	$835.25	$835.20