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	$54.52	8.636%	$59.2283	$59.23	$59.25	$59.20
Purchase #2	$125.47	6.822%	$134.0296	$134.03	$134.05	$134.00
Purchase #3	$181.28	3.268%	$187.2042	$187.20	$187.20	$187.20
Purchase #4	$248.43	3.867%	$258.0368	$258.04	$258.05	$258.00
Purchase #5	$113.91	8.717%	$123.8395	$123.84	$123.85	$123.80
Purchase #6	$140.81	10.384%	$155.4317	$155.43	$155.45	$155.40
Purchase #7	$74.75	9.632%	$81.9499	$81.95	$81.95	$81.90
7 purchase totals =	$939.17		$999.7200	$999.72	$999.80	$999.50