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	$73.80	4.569%	$77.1719	$77.17	$77.15	$77.20
Purchase #2	$39.82	10.531%	$44.0134	$44.01	$44.00	$44.00
Purchase #3	$111.97	7.575%	$120.4517	$120.45	$120.45	$120.50
Purchase #4	$116.86	12.811%	$131.8309	$131.83	$131.85	$131.80
Purchase #5	$83.97	7.763%	$90.4886	$90.49	$90.50	$90.50
Purchase #6	$158.96	6.270%	$168.9268	$168.93	$168.95	$168.90
Purchase #7	$143.51	13.512%	$162.9011	$162.90	$162.90	$162.90
7 purchase totals =	$728.89		$795.7844	$795.78	$795.80	$795.80