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	$150.47	4.666%	$157.4909	$157.49	$157.50	$157.50
Purchase #2	$77.77	4.453%	$81.2331	$81.23	$81.25	$81.20
Purchase #3	$38.96	13.128%	$44.0747	$44.07	$44.05	$44.10
Purchase #4	$65.86	9.788%	$72.3064	$72.31	$72.30	$72.30
Purchase #5	$103.37	5.299%	$108.8476	$108.85	$108.85	$108.80
Purchase #6	$52.64	4.706%	$55.1172	$55.12	$55.10	$55.10
Purchase #7	$82.36	11.636%	$91.9434	$91.94	$91.95	$91.90
7 purchase totals =	$571.43		$611.0133	$611.01	$611.00	$610.90