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	$140.30	10.353%	$154.8253	$154.83	$154.85	$154.80
Purchase #2	$171.71	10.724%	$190.1242	$190.12	$190.10	$190.10
Purchase #3	$156.98	3.721%	$162.8212	$162.82	$162.80	$162.80
Purchase #4	$216.33	11.625%	$241.4784	$241.48	$241.50	$241.50
Purchase #5	$123.77	10.276%	$136.4886	$136.49	$136.50	$136.50
Purchase #6	$144.44	12.718%	$162.8099	$162.81	$162.80	$162.80
Purchase #7	$184.86	13.623%	$210.0435	$210.04	$210.05	$210.00
7 purchase totals =	$1,138.39		$1,258.5911	$1,258.59	$1,258.60	$1,258.50