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	$212.39	3.522%	$219.8704	$219.87	$219.85	$219.90
Purchase #2	$205.32	9.752%	$225.3428	$225.34	$225.35	$225.30
Purchase #3	$115.50	13.778%	$131.4136	$131.41	$131.40	$131.40
Purchase #4	$90.78	12.646%	$102.26	$102.26	$102.25	$102.30
Purchase #5	$37.73	3.555%	$39.0713	$39.07	$39.05	$39.10
Purchase #6	$151.55	10.734%	$167.8174	$167.82	$167.80	$167.80
Purchase #7	$13.66	7.670%	$14.7077	$14.71	$14.70	$14.70
7 purchase totals =	$826.93		$900.4832	$900.48	$900.40	$900.50