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	$37.58	13.563%	$42.677	$42.68	$42.70	$42.70
Purchase #2	$67.30	4.556%	$70.3662	$70.37	$70.35	$70.40
Purchase #3	$71.51	9.172%	$78.0689	$78.07	$78.05	$78.10
Purchase #4	$73.51	13.789%	$83.6463	$83.65	$83.65	$83.60
Purchase #5	$31.70	6.866%	$33.8765	$33.88	$33.90	$33.90
Purchase #6	$34.87	4.170%	$36.3241	$36.32	$36.30	$36.30
Purchase #7	$201.56	3.255%	$208.1208	$208.12	$208.10	$208.10
7 purchase totals =	$518.03		$553.0798	$553.09	$553.05	$553.10