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	$53.70	4.852%	$56.3055	$56.31	$56.30	$56.30
Purchase #2	$169.93	7.201%	$182.1667	$182.17	$182.15	$182.20
Purchase #3	$233.66	3.393%	$241.5881	$241.59	$241.60	$241.60
Purchase #4	$25.98	13.188%	$29.4062	$29.41	$29.40	$29.40
Purchase #5	$166.72	4.857%	$174.8176	$174.82	$174.80	$174.80
Purchase #6	$135.70	8.109%	$146.7039	$146.70	$146.70	$146.70
Purchase #7	$84.81	7.162%	$90.8841	$90.88	$90.90	$90.90
7 purchase totals =	$870.50		$921.8721	$921.88	$921.85	$921.90