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	$103.47	4.858%	$108.4966	$108.50	$108.50	$108.50
Purchase #2	$228.95	13.189%	$259.1462	$259.15	$259.15	$259.10
Purchase #3	$179.85	5.371%	$189.5097	$189.51	$189.50	$189.50
Purchase #4	$179.34	3.181%	$185.0448	$185.04	$185.05	$185.00
Purchase #5	$37.60	7.414%	$40.3877	$40.39	$40.40	$40.40
Purchase #6	$238.33	10.525%	$263.4142	$263.41	$263.40	$263.40
Purchase #7	$35.78	6.658%	$38.1622	$38.16	$38.15	$38.20
7 purchase totals =	$1,003.32		$1,084.1614	$1,084.16	$1,084.15	$1,084.10