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	$52.83	6.719%	$56.3796	$56.38	$56.40	$56.40
Purchase #2	$164.39	3.518%	$170.1732	$170.17	$170.15	$170.20
Purchase #3	$241.39	9.402%	$264.0855	$264.09	$264.10	$264.10
Purchase #4	$228.32	11.690%	$255.0106	$255.01	$255.00	$255.00
Purchase #5	$17.78	10.691%	$19.6809	$19.68	$19.70	$19.70
Purchase #6	$127.73	3.197%	$131.8135	$131.81	$131.80	$131.80
Purchase #7	$133.81	7.477%	$143.815	$143.82	$143.80	$143.80
7 purchase totals =	$966.25		$1,040.9583	$1,040.96	$1,040.95	$1,041.00