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	$131.53	5.801%	$139.1601	$139.16	$139.15	$139.20
Purchase #2	$78.84	4.107%	$82.078	$82.08	$82.10	$82.10
Purchase #3	$60.67	4.599%	$63.4602	$63.46	$63.45	$63.50
Purchase #4	$149.43	10.115%	$164.5448	$164.54	$164.55	$164.50
Purchase #5	$187.32	10.317%	$206.6458	$206.65	$206.65	$206.60
Purchase #6	$107.32	3.612%	$111.1964	$111.20	$111.20	$111.20
Purchase #7	$152.93	13.341%	$173.3324	$173.33	$173.35	$173.30
7 purchase totals =	$868.04		$940.4177	$940.42	$940.45	$940.40