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	$35.41	8.391%	$38.3813	$38.38	$38.40	$38.40
Purchase #2	$74.47	7.730%	$80.2265	$80.23	$80.25	$80.20
Purchase #3	$100.49	12.637%	$113.1889	$113.19	$113.20	$113.20
Purchase #4	$51.83	4.704%	$54.2681	$54.27	$54.25	$54.30
Purchase #5	$232.67	9.341%	$254.4037	$254.40	$254.40	$254.40
Purchase #6	$122.56	12.532%	$137.9192	$137.92	$137.90	$137.90
Purchase #7	$74.99	10.301%	$82.7147	$82.71	$82.70	$82.70
7 purchase totals =	$692.42		$761.1024	$761.10	$761.10	$761.10