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	$134.64	11.284%	$149.8328	$149.83	$149.85	$149.80
Purchase #2	$171.30	11.401%	$190.8299	$190.83	$190.85	$190.80
Purchase #3	$111.89	11.323%	$124.5593	$124.56	$124.55	$124.60
Purchase #4	$198.71	13.500%	$225.5359	$225.54	$225.55	$225.50
Purchase #5	$19.88	12.648%	$22.3944	$22.39	$22.40	$22.40
Purchase #6	$39.75	6.553%	$42.3548	$42.35	$42.35	$42.40
Purchase #7	$137.91	4.419%	$144.0042	$144.00	$144.00	$144.00
7 purchase totals =	$814.08		$899.5113	$899.50	$899.55	$899.50