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	$33.45	8.664%	$36.3481	$36.35	$36.35	$36.30
Purchase #2	$164.95	4.299%	$172.0412	$172.04	$172.05	$172.00
Purchase #3	$170.27	13.429%	$193.1356	$193.14	$193.15	$193.10
Purchase #4	$156.36	10.107%	$172.1633	$172.16	$172.15	$172.20
Purchase #5	$40.49	4.395%	$42.2695	$42.27	$42.25	$42.30
Purchase #6	$104.38	6.643%	$111.314	$111.31	$111.30	$111.30
Purchase #7	$76.58	7.501%	$82.3243	$82.32	$82.30	$82.30
7 purchase totals =	$746.48		$809.5960	$809.59	$809.55	$809.50