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	$56.33	11.447%	$62.7781	$62.78	$62.80	$62.80
Purchase #2	$49.87	6.300%	$53.0118	$53.01	$53.00	$53.00
Purchase #3	$49.33	12.691%	$55.5905	$55.59	$55.60	$55.60
Purchase #4	$179.32	9.582%	$196.5024	$196.50	$196.50	$196.50
Purchase #5	$74.71	7.855%	$80.5785	$80.58	$80.60	$80.60
Purchase #6	$207.26	10.801%	$229.6462	$229.65	$229.65	$229.60
Purchase #7	$36.39	10.810%	$40.3238	$40.32	$40.30	$40.30
7 purchase totals =	$653.21		$718.4313	$718.43	$718.45	$718.40