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	$17.60	12.402%	$19.7828	$19.78	$19.80	$19.80
Purchase #2	$179.33	9.798%	$196.9008	$196.90	$196.90	$196.90
Purchase #3	$122.69	12.188%	$137.6435	$137.64	$137.65	$137.60
Purchase #4	$161.81	12.678%	$182.3243	$182.32	$182.30	$182.30
Purchase #5	$96.77	4.201%	$100.8353	$100.84	$100.85	$100.80
Purchase #6	$231.74	5.128%	$243.6236	$243.62	$243.60	$243.60
Purchase #7	$46.25	12.816%	$52.1774	$52.18	$52.20	$52.20
7 purchase totals =	$856.19		$933.2877	$933.28	$933.30	$933.20