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	$64.34	12.146%	$72.1547	$72.15	$72.15	$72.20
Purchase #2	$144.40	9.792%	$158.5396	$158.54	$158.55	$158.50
Purchase #3	$26.56	11.112%	$29.5113	$29.51	$29.50	$29.50
Purchase #4	$126.56	10.182%	$139.4463	$139.45	$139.45	$139.40
Purchase #5	$173.49	10.639%	$191.9476	$191.95	$191.95	$191.90
Purchase #6	$92.34	3.641%	$95.7021	$95.70	$95.70	$95.70
Purchase #7	$237.33	6.249%	$252.1608	$252.16	$252.15	$252.20
7 purchase totals =	$865.02		$939.4624	$939.46	$939.45	$939.40