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	$19.65	3.178%	$20.2745	$20.27	$20.25	$20.30
Purchase #2	$164.76	10.761%	$182.4898	$182.49	$182.50	$182.50
Purchase #3	$143.73	6.791%	$153.4907	$153.49	$153.50	$153.50
Purchase #4	$109.46	3.644%	$113.4487	$113.45	$113.45	$113.40
Purchase #5	$93.58	10.242%	$103.1645	$103.16	$103.15	$103.20
Purchase #6	$159.61	3.729%	$165.5619	$165.56	$165.55	$165.60
Purchase #7	$194.58	3.610%	$201.6043	$201.60	$201.60	$201.60
7 purchase totals =	$885.37		$940.0344	$940.02	$940.00	$940.10