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	$86.78	4.795%	$90.9411	$90.94	$90.95	$90.90
Purchase #2	$154.54	5.416%	$162.9099	$162.91	$162.90	$162.90
Purchase #3	$180.82	12.514%	$203.4478	$203.45	$203.45	$203.40
Purchase #4	$34.93	13.254%	$39.5596	$39.56	$39.55	$39.60
Purchase #5	$108.66	5.718%	$114.8732	$114.87	$114.85	$114.90
Purchase #6	$52.61	4.118%	$54.7765	$54.78	$54.80	$54.80
Purchase #7	$7.42	5.176%	$7.8041	$7.80	$7.80	$7.80
7 purchase totals =	$625.76		$674.3122	$674.31	$674.30	$674.30