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	$203.93	4.840%	$213.8002	$213.80	$213.80	$213.80
Purchase #2	$215.70	9.221%	$235.5897	$235.59	$235.60	$235.60
Purchase #3	$80.58	7.386%	$86.5316	$86.53	$86.55	$86.50
Purchase #4	$123.39	3.329%	$127.4977	$127.50	$127.50	$127.50
Purchase #5	$166.90	11.357%	$185.8548	$185.85	$185.85	$185.90
Purchase #6	$233.60	13.770%	$265.7667	$265.77	$265.75	$265.80
Purchase #7	$214.77	7.151%	$230.1282	$230.13	$230.15	$230.10
7 purchase totals =	$1,238.87		$1,345.1689	$1,345.17	$1,345.20	$1,345.20