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	$247.88	9.758%	$272.0681	$272.07	$272.05	$272.10
Purchase #2	$108.28	13.724%	$123.1403	$123.14	$123.15	$123.10
Purchase #3	$79.57	7.353%	$85.4208	$85.42	$85.40	$85.40
Purchase #4	$145.81	7.662%	$156.982	$156.98	$157.00	$157.00
Purchase #5	$108.82	9.426%	$119.0774	$119.08	$119.10	$119.10
Purchase #6	$105.59	4.820%	$110.6794	$110.68	$110.70	$110.70
Purchase #7	$119.36	10.469%	$131.8558	$131.86	$131.85	$131.90
7 purchase totals =	$915.31		$999.2238	$999.23	$999.25	$999.30