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	$47.25	12.227%	$53.0273	$53.03	$53.05	$53.00
Purchase #2	$55.52	7.677%	$59.7823	$59.78	$59.80	$59.80
Purchase #3	$125.60	9.763%	$137.8623	$137.86	$137.85	$137.90
Purchase #4	$101.76	7.480%	$109.3716	$109.37	$109.35	$109.40
Purchase #5	$27.35	9.113%	$29.8424	$29.84	$29.85	$29.80
Purchase #6	$34.56	9.782%	$37.9407	$37.94	$37.95	$37.90
Purchase #7	$152.45	3.804%	$158.2492	$158.25	$158.25	$158.20
7 purchase totals =	$544.49		$586.0758	$586.07	$586.10	$586.00