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	$166.78	5.463%	$175.8912	$175.89	$175.90	$175.90
Purchase #2	$34.60	9.795%	$37.9891	$37.99	$38.00	$38.00
Purchase #3	$17.84	9.181%	$19.4779	$19.48	$19.50	$19.50
Purchase #4	$172.31	4.219%	$179.5798	$179.58	$179.60	$179.60
Purchase #5	$233.41	10.571%	$258.0838	$258.08	$258.10	$258.10
Purchase #6	$208.77	6.168%	$221.6469	$221.65	$221.65	$221.60
Purchase #7	$142.89	5.310%	$150.4775	$150.48	$150.50	$150.50
7 purchase totals =	$976.60		$1,043.1462	$1,043.15	$1,043.25	$1,043.20