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	$70.50	3.307%	$72.8314	$72.83	$72.85	$72.80
Purchase #2	$159.51	6.514%	$169.9005	$169.90	$169.90	$169.90
Purchase #3	$158.93	8.243%	$172.0306	$172.03	$172.05	$172.00
Purchase #4	$21.61	12.771%	$24.3698	$24.37	$24.35	$24.40
Purchase #5	$120.45	9.695%	$132.1276	$132.13	$132.15	$132.10
Purchase #6	$66.69	9.113%	$72.7675	$72.77	$72.75	$72.80
Purchase #7	$226.66	3.680%	$235.0011	$235.00	$235.00	$235.00
7 purchase totals =	$824.35		$879.0285	$879.03	$879.05	$879.00