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	$50.27	13.566%	$57.0896	$57.09	$57.10	$57.10
Purchase #2	$10.94	9.518%	$11.9813	$11.98	$12.00	$12.00
Purchase #3	$50.39	6.799%	$53.816	$53.82	$53.80	$53.80
Purchase #4	$162.37	3.298%	$167.725	$167.73	$167.75	$167.70
Purchase #5	$241.97	5.278%	$254.7412	$254.74	$254.75	$254.70
Purchase #6	$153.34	3.557%	$158.7943	$158.79	$158.80	$158.80
Purchase #7	$137.83	3.306%	$142.3867	$142.39	$142.40	$142.40
7 purchase totals =	$807.11		$846.5341	$846.54	$846.60	$846.50