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	$41.87	4.856%	$43.9032	$43.90	$43.90	$43.90
Purchase #2	$64.47	4.180%	$67.1648	$67.16	$67.15	$67.20
Purchase #3	$228.46	13.665%	$259.6791	$259.68	$259.70	$259.70
Purchase #4	$190.98	4.177%	$198.9572	$198.96	$198.95	$199.00
Purchase #5	$107.36	6.666%	$114.5166	$114.52	$114.50	$114.50
Purchase #6	$69.91	12.690%	$78.7816	$78.78	$78.80	$78.80
Purchase #7	$230.63	4.616%	$241.2759	$241.28	$241.30	$241.30
7 purchase totals =	$933.68		$1,004.2784	$1,004.28	$1,004.30	$1,004.40