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	$228.42	13.788%	$259.9145	$259.91	$259.90	$259.90
Purchase #2	$146.60	12.177%	$164.4515	$164.45	$164.45	$164.50
Purchase #3	$178.82	10.829%	$198.1844	$198.18	$198.20	$198.20
Purchase #4	$40.49	4.547%	$42.3311	$42.33	$42.35	$42.30
Purchase #5	$234.65	3.383%	$242.5882	$242.59	$242.60	$242.60
Purchase #6	$139.35	8.530%	$151.2366	$151.24	$151.25	$151.20
Purchase #7	$155.34	12.606%	$174.9222	$174.92	$174.90	$174.90
7 purchase totals =	$1,123.67		$1,233.6285	$1,233.62	$1,233.65	$1,233.60