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	$68.58	13.761%	$78.0173	$78.02	$78.00	$78.00
Purchase #2	$97.35	12.435%	$109.4555	$109.46	$109.45	$109.50
Purchase #3	$66.73	3.224%	$68.8814	$68.88	$68.90	$68.90
Purchase #4	$154.76	8.190%	$167.4348	$167.43	$167.45	$167.40
Purchase #5	$59.58	5.278%	$62.7246	$62.72	$62.70	$62.70
Purchase #6	$121.30	9.598%	$132.9424	$132.94	$132.95	$132.90
Purchase #7	$205.27	7.376%	$220.4107	$220.41	$220.40	$220.40
7 purchase totals =	$773.57		$839.8667	$839.86	$839.85	$839.80