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	$59.54	12.193%	$66.7997	$66.80	$66.80	$66.80
Purchase #2	$218.51	11.860%	$244.4253	$244.43	$244.45	$244.40
Purchase #3	$44.88	8.666%	$48.7693	$48.77	$48.75	$48.80
Purchase #4	$44.72	12.820%	$50.4531	$50.45	$50.45	$50.50
Purchase #5	$38.52	3.676%	$39.936	$39.94	$39.95	$39.90
Purchase #6	$26.52	12.854%	$29.9289	$29.93	$29.95	$29.90
Purchase #7	$78.82	11.682%	$88.0278	$88.03	$88.05	$88.00
7 purchase totals =	$511.51		$568.3401	$568.35	$568.40	$568.30