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	$190.71	11.822%	$213.2557	$213.26	$213.25	$213.30
Purchase #2	$123.58	11.808%	$138.1723	$138.17	$138.15	$138.20
Purchase #3	$228.80	12.565%	$257.5487	$257.55	$257.55	$257.50
Purchase #4	$140.69	3.734%	$145.9434	$145.94	$145.95	$145.90
Purchase #5	$81.82	9.698%	$89.7549	$89.75	$89.75	$89.80
Purchase #6	$32.39	4.479%	$33.8407	$33.84	$33.85	$33.80
Purchase #7	$69.90	11.595%	$78.0049	$78.00	$78.00	$78.00
7 purchase totals =	$867.89		$956.5206	$956.51	$956.50	$956.50