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	$7.25	5.402%	$7.6416	$7.64	$7.65	$7.60
Purchase #2	$164.60	4.270%	$171.6284	$171.63	$171.65	$171.60
Purchase #3	$121.49	4.873%	$127.4102	$127.41	$127.40	$127.40
Purchase #4	$69.32	13.252%	$78.5063	$78.51	$78.50	$78.50
Purchase #5	$124.68	13.790%	$141.8734	$141.87	$141.85	$141.90
Purchase #6	$147.65	7.380%	$158.5466	$158.55	$158.55	$158.50
Purchase #7	$50.90	11.587%	$56.7978	$56.80	$56.80	$56.80
7 purchase totals =	$685.89		$742.4043	$742.41	$742.40	$742.30