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	$65.69	6.872%	$70.2042	$70.20	$70.20	$70.20
Purchase #2	$130.93	10.326%	$144.4498	$144.45	$144.45	$144.40
Purchase #3	$127.50	3.410%	$131.8478	$131.85	$131.85	$131.80
Purchase #4	$94.38	12.102%	$105.8019	$105.80	$105.80	$105.80
Purchase #5	$53.54	6.758%	$57.1582	$57.16	$57.15	$57.20
Purchase #6	$158.85	9.757%	$174.349	$174.35	$174.35	$174.30
Purchase #7	$200.89	12.749%	$226.5015	$226.50	$226.50	$226.50
7 purchase totals =	$831.78		$910.3124	$910.31	$910.30	$910.20