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	$48.82	7.514%	$52.4883	$52.49	$52.50	$52.50
Purchase #2	$173.40	3.646%	$179.7222	$179.72	$179.70	$179.70
Purchase #3	$218.85	13.837%	$249.1323	$249.13	$249.15	$249.10
Purchase #4	$224.80	13.703%	$255.6043	$255.60	$255.60	$255.60
Purchase #5	$72.72	5.655%	$76.8323	$76.83	$76.85	$76.80
Purchase #6	$90.36	10.546%	$99.8894	$99.89	$99.90	$99.90
Purchase #7	$197.92	3.665%	$205.1738	$205.17	$205.15	$205.20
7 purchase totals =	$1,026.87		$1,118.8426	$1,118.83	$1,118.85	$1,118.80