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	$59.49	13.523%	$67.5348	$67.53	$67.55	$67.50
Purchase #2	$46.28	6.695%	$49.3784	$49.38	$49.40	$49.40
Purchase #3	$246.91	10.826%	$273.6405	$273.64	$273.65	$273.60
Purchase #4	$67.68	6.453%	$72.0474	$72.05	$72.05	$72.00
Purchase #5	$243.70	6.115%	$258.6023	$258.60	$258.60	$258.60
Purchase #6	$37.43	4.595%	$39.1499	$39.15	$39.15	$39.10
Purchase #7	$135.91	3.384%	$140.5092	$140.51	$140.50	$140.50
7 purchase totals =	$837.40		$900.8625	$900.86	$900.90	$900.70