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	$81.83	6.370%	$87.0426	$87.04	$87.05	$87.00
Purchase #2	$129.77	7.814%	$139.9102	$139.91	$139.90	$139.90
Purchase #3	$152.94	3.477%	$158.2577	$158.26	$158.25	$158.30
Purchase #4	$78.45	10.284%	$86.5178	$86.52	$86.50	$86.50
Purchase #5	$160.42	6.837%	$171.3879	$171.39	$171.40	$171.40
Purchase #6	$11.76	6.597%	$12.5358	$12.54	$12.55	$12.50
Purchase #7	$48.84	10.263%	$53.8524	$53.85	$53.85	$53.90
7 purchase totals =	$664.01		$709.5044	$709.51	$709.50	$709.50