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	$150.94	4.233%	$157.3293	$157.33	$157.35	$157.30
Purchase #2	$29.61	4.724%	$31.0088	$31.01	$31.00	$31.00
Purchase #3	$248.94	9.852%	$273.4656	$273.47	$273.45	$273.50
Purchase #4	$83.94	13.787%	$95.5128	$95.51	$95.50	$95.50
Purchase #5	$198.27	6.356%	$210.872	$210.87	$210.85	$210.90
Purchase #6	$143.75	6.842%	$153.5854	$153.59	$153.60	$153.60
Purchase #7	$238.92	13.485%	$271.1384	$271.14	$271.15	$271.10
7 purchase totals =	$1,094.37		$1,192.9123	$1,192.92	$1,192.90	$1,192.90