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	$163.69	4.581%	$171.1886	$171.19	$171.20	$171.20
Purchase #2	$99.86	3.581%	$103.436	$103.44	$103.45	$103.40
Purchase #3	$33.80	10.659%	$37.4027	$37.40	$37.40	$37.40
Purchase #4	$227.39	6.493%	$242.1544	$242.15	$242.15	$242.20
Purchase #5	$96.51	5.614%	$101.9281	$101.93	$101.95	$101.90
Purchase #6	$78.51	12.403%	$88.2476	$88.25	$88.25	$88.20
Purchase #7	$214.30	7.724%	$230.8525	$230.85	$230.85	$230.90
7 purchase totals =	$914.06		$975.2099	$975.21	$975.25	$975.20