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	$99.99	11.430%	$111.4189	$111.42	$111.40	$111.40
Purchase #2	$48.41	7.532%	$52.0562	$52.06	$52.05	$52.10
Purchase #3	$34.93	7.848%	$37.6713	$37.67	$37.65	$37.70
Purchase #4	$250.95	4.179%	$261.4372	$261.44	$261.45	$261.40
Purchase #5	$156.86	13.340%	$177.7851	$177.79	$177.80	$177.80
Purchase #6	$81.79	13.196%	$92.583	$92.58	$92.60	$92.60
Purchase #7	$90.85	12.622%	$102.3171	$102.32	$102.30	$102.30
7 purchase totals =	$763.78		$835.2688	$835.28	$835.25	$835.30