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	$36.67	4.868%	$38.4551	$38.46	$38.45	$38.50
Purchase #2	$172.86	13.405%	$196.0319	$196.03	$196.05	$196.00
Purchase #3	$86.87	3.672%	$90.0599	$90.06	$90.05	$90.10
Purchase #4	$14.97	4.585%	$15.6564	$15.66	$15.65	$15.70
Purchase #5	$74.38	5.462%	$78.4426	$78.44	$78.45	$78.40
Purchase #6	$117.74	12.251%	$132.1643	$132.16	$132.15	$132.20
Purchase #7	$5.76	6.476%	$6.133	$6.13	$6.15	$6.10
7 purchase totals =	$509.25		$556.9432	$556.94	$556.95	$557.00