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	$234.33	9.582%	$256.7835	$256.78	$256.80	$256.80
Purchase #2	$61.68	4.438%	$64.4174	$64.42	$64.40	$64.40
Purchase #3	$167.77	4.134%	$174.7056	$174.71	$174.70	$174.70
Purchase #4	$105.29	4.104%	$109.6111	$109.61	$109.60	$109.60
Purchase #5	$15.80	12.238%	$17.7336	$17.73	$17.75	$17.70
Purchase #6	$101.76	6.611%	$108.4874	$108.49	$108.50	$108.50
Purchase #7	$176.76	4.748%	$185.1526	$185.15	$185.15	$185.20
7 purchase totals =	$863.39		$916.8912	$916.89	$916.90	$916.90