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	$25.94	5.588%	$27.3895	$27.39	$27.40	$27.40
Purchase #2	$123.93	3.103%	$127.7755	$127.78	$127.80	$127.80
Purchase #3	$47.72	9.635%	$52.3178	$52.32	$52.30	$52.30
Purchase #4	$208.92	7.347%	$224.2694	$224.27	$224.25	$224.30
Purchase #5	$65.95	9.697%	$72.3452	$72.35	$72.35	$72.30
Purchase #6	$42.52	4.384%	$44.3841	$44.38	$44.40	$44.40
Purchase #7	$203.85	10.588%	$225.4336	$225.43	$225.45	$225.40
7 purchase totals =	$718.83		$773.9151	$773.92	$773.95	$773.90