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	$53.66	4.161%	$55.8928	$55.89	$55.90	$55.90
Purchase #2	$48.64	10.406%	$53.7015	$53.70	$53.70	$53.70
Purchase #3	$217.68	11.830%	$243.4315	$243.43	$243.45	$243.40
Purchase #4	$86.39	4.107%	$89.938	$89.94	$89.95	$89.90
Purchase #5	$6.49	13.320%	$7.3545	$7.35	$7.35	$7.40
Purchase #6	$33.34	6.733%	$35.5848	$35.58	$35.60	$35.60
Purchase #7	$83.54	10.656%	$92.442	$92.44	$92.45	$92.40
7 purchase totals =	$529.74		$578.3451	$578.33	$578.40	$578.30