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	$49.79	13.263%	$56.3936	$56.39	$56.40	$56.40
Purchase #2	$173.45	9.230%	$189.4594	$189.46	$189.45	$189.50
Purchase #3	$75.91	3.151%	$78.3019	$78.30	$78.30	$78.30
Purchase #4	$207.86	9.464%	$227.5319	$227.53	$227.55	$227.50
Purchase #5	$139.91	12.857%	$157.8982	$157.90	$157.90	$157.90
Purchase #6	$55.71	10.157%	$61.3685	$61.37	$61.35	$61.40
Purchase #7	$100.65	5.166%	$105.8496	$105.85	$105.85	$105.80
7 purchase totals =	$803.28		$876.8031	$876.80	$876.80	$876.80