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	$171.95	6.299%	$182.7811	$182.78	$182.80	$182.80
Purchase #2	$153.39	3.250%	$158.3752	$158.38	$158.40	$158.40
Purchase #3	$179.47	8.533%	$194.7842	$194.78	$194.80	$194.80
Purchase #4	$172.43	13.701%	$196.0546	$196.05	$196.05	$196.10
Purchase #5	$240.46	13.162%	$272.1093	$272.11	$272.10	$272.10
Purchase #6	$201.37	9.813%	$221.1304	$221.13	$221.15	$221.10
Purchase #7	$131.83	9.578%	$144.4567	$144.46	$144.45	$144.50
7 purchase totals =	$1,250.90		$1,369.6915	$1,369.69	$1,369.75	$1,369.80