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	$70.89	8.293%	$76.7689	$76.77	$76.75	$76.80
Purchase #2	$98.40	12.807%	$111.0021	$111.00	$111.00	$111.00
Purchase #3	$131.56	9.842%	$144.5081	$144.51	$144.50	$144.50
Purchase #4	$133.53	12.772%	$150.5845	$150.58	$150.60	$150.60
Purchase #5	$36.88	12.513%	$41.4948	$41.49	$41.50	$41.50
Purchase #6	$17.40	6.265%	$18.4901	$18.49	$18.50	$18.50
Purchase #7	$90.75	11.625%	$101.2997	$101.30	$101.30	$101.30
7 purchase totals =	$579.41		$644.1482	$644.14	$644.15	$644.20