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	$70.41	11.761%	$78.6909	$78.69	$78.70	$78.70
Purchase #2	$11.74	10.308%	$12.9502	$12.95	$12.95	$13.00
Purchase #3	$168.75	13.414%	$191.3861	$191.39	$191.40	$191.40
Purchase #4	$110.97	6.355%	$118.0221	$118.02	$118.00	$118.00
Purchase #5	$164.45	13.733%	$187.0339	$187.03	$187.05	$187.00
Purchase #6	$33.81	13.136%	$38.2513	$38.25	$38.25	$38.30
Purchase #7	$161.72	6.356%	$171.9989	$172.00	$172.00	$172.00
7 purchase totals =	$721.85		$798.3334	$798.33	$798.35	$798.40