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	$37.37	6.255%	$39.7075	$39.71	$39.70	$39.70
Purchase #2	$187.90	9.389%	$205.5419	$205.54	$205.55	$205.50
Purchase #3	$17.92	13.329%	$20.3086	$20.31	$20.30	$20.30
Purchase #4	$182.83	9.632%	$200.4402	$200.44	$200.45	$200.40
Purchase #5	$121.76	9.121%	$132.8657	$132.87	$132.85	$132.90
Purchase #6	$140.99	8.812%	$153.414	$153.41	$153.40	$153.40
Purchase #7	$31.51	3.267%	$32.5394	$32.54	$32.55	$32.50
7 purchase totals =	$720.28		$784.8173	$784.82	$784.80	$784.70