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	$78.32	12.790%	$88.3371	$88.34	$88.35	$88.30
Purchase #2	$217.61	9.738%	$238.8009	$238.80	$238.80	$238.80
Purchase #3	$47.87	8.208%	$51.7992	$51.80	$51.80	$51.80
Purchase #4	$48.80	5.698%	$51.5806	$51.58	$51.60	$51.60
Purchase #5	$38.30	13.381%	$43.4249	$43.42	$43.40	$43.40
Purchase #6	$46.91	12.716%	$52.8751	$52.88	$52.90	$52.90
Purchase #7	$206.89	9.172%	$225.866	$225.87	$225.85	$225.90
7 purchase totals =	$684.70		$752.6838	$752.69	$752.70	$752.70