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	$59.73	10.685%	$66.1122	$66.11	$66.10	$66.10
Purchase #2	$240.43	3.387%	$248.5734	$248.57	$248.55	$248.60
Purchase #3	$36.91	8.858%	$40.1795	$40.18	$40.20	$40.20
Purchase #4	$169.31	13.476%	$192.1262	$192.13	$192.15	$192.10
Purchase #5	$12.93	3.427%	$13.3731	$13.37	$13.35	$13.40
Purchase #6	$17.33	6.687%	$18.4889	$18.49	$18.50	$18.50
Purchase #7	$64.36	12.786%	$72.5891	$72.59	$72.60	$72.60
7 purchase totals =	$601.00		$651.4424	$651.44	$651.45	$651.50