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	$119.71	3.399%	$123.7789	$123.78	$123.80	$123.80
Purchase #2	$43.51	3.264%	$44.9302	$44.93	$44.95	$44.90
Purchase #3	$31.69	9.524%	$34.7082	$34.71	$34.70	$34.70
Purchase #4	$117.94	4.359%	$123.081	$123.08	$123.10	$123.10
Purchase #5	$68.54	5.293%	$72.1678	$72.17	$72.15	$72.20
Purchase #6	$20.43	4.262%	$21.3007	$21.30	$21.30	$21.30
Purchase #7	$102.29	5.411%	$107.8249	$107.82	$107.80	$107.80
7 purchase totals =	$504.11		$527.7917	$527.79	$527.80	$527.80