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	$46.92	5.443%	$49.4739	$49.47	$49.45	$49.50
Purchase #2	$80.59	6.370%	$85.7236	$85.72	$85.70	$85.70
Purchase #3	$104.94	12.711%	$118.2789	$118.28	$118.30	$118.30
Purchase #4	$43.31	4.111%	$45.0905	$45.09	$45.10	$45.10
Purchase #5	$7.71	5.472%	$8.1319	$8.13	$8.15	$8.10
Purchase #6	$144.86	4.482%	$151.3526	$151.35	$151.35	$151.40
Purchase #7	$66.48	7.688%	$71.591	$71.59	$71.60	$71.60
7 purchase totals =	$494.81		$529.6424	$529.63	$529.65	$529.70