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	$166.88	11.340%	$185.8042	$185.80	$185.80	$185.80
Purchase #2	$154.78	13.857%	$176.2279	$176.23	$176.25	$176.20
Purchase #3	$119.55	7.496%	$128.5115	$128.51	$128.50	$128.50
Purchase #4	$138.82	9.724%	$152.3189	$152.32	$152.30	$152.30
Purchase #5	$44.82	8.809%	$48.7682	$48.77	$48.75	$48.80
Purchase #6	$95.79	5.137%	$100.7107	$100.71	$100.70	$100.70
Purchase #7	$25.65	7.151%	$27.4842	$27.48	$27.50	$27.50
7 purchase totals =	$746.29		$819.8256	$819.82	$819.80	$819.80