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	$229.39	12.610%	$258.3161	$258.32	$258.30	$258.30
Purchase #2	$236.68	4.146%	$246.4928	$246.49	$246.50	$246.50
Purchase #3	$176.43	7.532%	$189.7187	$189.72	$189.70	$189.70
Purchase #4	$60.84	6.786%	$64.9686	$64.97	$64.95	$65.00
Purchase #5	$87.56	3.143%	$90.312	$90.31	$90.30	$90.30
Purchase #6	$22.43	13.715%	$25.5063	$25.51	$25.50	$25.50
Purchase #7	$105.75	3.606%	$109.5633	$109.56	$109.55	$109.60
7 purchase totals =	$919.08		$984.8778	$984.88	$984.80	$984.90