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	$16.81	10.523%	$18.5789	$18.58	$18.60	$18.60
Purchase #2	$156.30	10.531%	$172.76	$172.76	$172.75	$172.80
Purchase #3	$165.60	10.568%	$183.1006	$183.10	$183.10	$183.10
Purchase #4	$95.46	5.658%	$100.8611	$100.86	$100.85	$100.90
Purchase #5	$80.47	6.349%	$85.579	$85.58	$85.60	$85.60
Purchase #6	$171.98	6.778%	$183.6368	$183.64	$183.65	$183.60
Purchase #7	$183.46	9.413%	$200.7291	$200.73	$200.75	$200.70
7 purchase totals =	$870.08		$945.2455	$945.25	$945.30	$945.30