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	$238.38	11.797%	$266.5017	$266.50	$266.50	$266.50
Purchase #2	$169.78	6.796%	$181.3182	$181.32	$181.30	$181.30
Purchase #3	$134.59	7.429%	$144.5887	$144.59	$144.60	$144.60
Purchase #4	$206.62	10.292%	$227.8853	$227.89	$227.90	$227.90
Purchase #5	$98.29	10.756%	$108.8621	$108.86	$108.85	$108.90
Purchase #6	$47.33	5.336%	$49.8555	$49.86	$49.85	$49.90
Purchase #7	$148.95	11.599%	$166.2267	$166.23	$166.25	$166.20
7 purchase totals =	$1,043.94		$1,145.2382	$1,145.25	$1,145.25	$1,145.30