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	$59.81	8.492%	$64.8891	$64.89	$64.90	$64.90
Purchase #2	$155.40	13.634%	$176.5872	$176.59	$176.60	$176.60
Purchase #3	$175.54	8.454%	$190.3802	$190.38	$190.40	$190.40
Purchase #4	$138.64	12.544%	$156.031	$156.03	$156.05	$156.00
Purchase #5	$156.61	5.506%	$165.2329	$165.23	$165.25	$165.20
Purchase #6	$38.71	6.601%	$41.2652	$41.27	$41.25	$41.30
Purchase #7	$196.42	3.762%	$203.8093	$203.81	$203.80	$203.80
7 purchase totals =	$921.13		$998.1949	$998.20	$998.25	$998.20