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	$46.84	7.317%	$50.2673	$50.27	$50.25	$50.30
Purchase #2	$45.54	5.106%	$47.8653	$47.87	$47.85	$47.90
Purchase #3	$134.78	12.564%	$151.7138	$151.71	$151.70	$151.70
Purchase #4	$123.31	6.618%	$131.4707	$131.47	$131.45	$131.50
Purchase #5	$102.70	13.167%	$116.2225	$116.22	$116.20	$116.20
Purchase #6	$85.65	13.701%	$97.3849	$97.38	$97.40	$97.40
Purchase #7	$73.89	9.652%	$81.0219	$81.02	$81.00	$81.00
7 purchase totals =	$612.71		$675.9464	$675.94	$675.85	$676.00