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	$230.59	13.133%	$260.8734	$260.87	$260.85	$260.90
Purchase #2	$20.78	5.396%	$21.9013	$21.90	$21.90	$21.90
Purchase #3	$150.94	12.675%	$170.0716	$170.07	$170.05	$170.10
Purchase #4	$45.91	4.229%	$47.8515	$47.85	$47.85	$47.90
Purchase #5	$88.97	12.563%	$100.1473	$100.15	$100.15	$100.10
Purchase #6	$21.49	4.680%	$22.4957	$22.50	$22.50	$22.50
Purchase #7	$48.50	7.706%	$52.2374	$52.24	$52.25	$52.20
7 purchase totals =	$607.18		$675.5782	$675.58	$675.55	$675.60