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	$123.64	13.193%	$139.9518	$139.95	$139.95	$140.00
Purchase #2	$72.52	8.720%	$78.8437	$78.84	$78.85	$78.80
Purchase #3	$53.43	5.810%	$56.5343	$56.53	$56.55	$56.50
Purchase #4	$168.61	11.745%	$188.4132	$188.41	$188.40	$188.40
Purchase #5	$6.77	11.106%	$7.5219	$7.52	$7.50	$7.50
Purchase #6	$65.61	13.502%	$74.4687	$74.47	$74.45	$74.50
Purchase #7	$31.35	8.562%	$34.0342	$34.03	$34.05	$34.00
7 purchase totals =	$521.93		$579.7678	$579.75	$579.75	$579.70