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	$55.52	3.652%	$57.5476	$57.55	$57.55	$57.50
Purchase #2	$81.89	10.434%	$90.4344	$90.43	$90.45	$90.40
Purchase #3	$208.64	6.736%	$222.694	$222.69	$222.70	$222.70
Purchase #4	$226.82	3.659%	$235.1193	$235.12	$235.10	$235.10
Purchase #5	$53.27	13.776%	$60.6085	$60.61	$60.60	$60.60
Purchase #6	$57.75	12.505%	$64.9716	$64.97	$64.95	$65.00
Purchase #7	$78.36	6.779%	$83.672	$83.67	$83.65	$83.70
7 purchase totals =	$762.25		$815.0474	$815.04	$815.00	$815.00