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	$37.76	4.541%	$39.4747	$39.47	$39.45	$39.50
Purchase #2	$42.95	11.530%	$47.9021	$47.90	$47.90	$47.90
Purchase #3	$34.96	8.477%	$37.9236	$37.92	$37.90	$37.90
Purchase #4	$146.83	7.730%	$158.18	$158.18	$158.20	$158.20
Purchase #5	$239.26	9.121%	$261.0829	$261.08	$261.10	$261.10
Purchase #6	$52.96	5.312%	$55.7732	$55.77	$55.75	$55.80
Purchase #7	$137.75	4.596%	$144.081	$144.08	$144.10	$144.10
7 purchase totals =	$692.47		$744.4175	$744.40	$744.40	$744.50