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	$37.99	7.466%	$40.8263	$40.83	$40.85	$40.80
Purchase #2	$176.98	6.363%	$188.2412	$188.24	$188.25	$188.20
Purchase #3	$188.76	9.463%	$206.6224	$206.62	$206.60	$206.60
Purchase #4	$104.67	7.116%	$112.1183	$112.12	$112.10	$112.10
Purchase #5	$150.47	3.177%	$155.2504	$155.25	$155.25	$155.30
Purchase #6	$215.75	3.126%	$222.4943	$222.49	$222.50	$222.50
Purchase #7	$145.55	4.798%	$152.5335	$152.53	$152.55	$152.50
7 purchase totals =	$1,020.17		$1,078.0864	$1,078.08	$1,078.10	$1,078.00