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	$39.54	12.597%	$44.5209	$44.52	$44.50	$44.50
Purchase #2	$100.55	10.403%	$111.0102	$111.01	$111.00	$111.00
Purchase #3	$94.77	6.351%	$100.7888	$100.79	$100.80	$100.80
Purchase #4	$67.79	6.696%	$72.3292	$72.33	$72.35	$72.30
Purchase #5	$142.75	9.493%	$156.3013	$156.30	$156.30	$156.30
Purchase #6	$64.80	6.239%	$68.8429	$68.84	$68.85	$68.80
Purchase #7	$121.26	4.827%	$127.1132	$127.11	$127.10	$127.10
7 purchase totals =	$631.46		$680.9065	$680.90	$680.90	$680.80