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	$104.88	9.172%	$114.4996	$114.50	$114.50	$114.50
Purchase #2	$71.62	11.860%	$80.1141	$80.11	$80.10	$80.10
Purchase #3	$56.64	10.143%	$62.385	$62.39	$62.40	$62.40
Purchase #4	$114.79	7.710%	$123.6403	$123.64	$123.65	$123.60
Purchase #5	$7.46	5.487%	$7.8693	$7.87	$7.85	$7.90
Purchase #6	$5.60	4.594%	$5.8573	$5.86	$5.85	$5.90
Purchase #7	$121.28	10.674%	$134.2254	$134.23	$134.25	$134.20
7 purchase totals =	$482.27		$528.5910	$528.60	$528.60	$528.60