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	$6.83	10.864%	$7.572	$7.57	$7.55	$7.60
Purchase #2	$69.87	12.374%	$78.5157	$78.52	$78.50	$78.50
Purchase #3	$34.93	8.564%	$37.9214	$37.92	$37.90	$37.90
Purchase #4	$126.51	13.816%	$143.9886	$143.99	$144.00	$144.00
Purchase #5	$147.39	5.596%	$155.6379	$155.64	$155.65	$155.60
Purchase #6	$50.79	6.450%	$54.066	$54.07	$54.05	$54.10
Purchase #7	$46.59	9.121%	$50.8395	$50.84	$50.85	$50.80
7 purchase totals =	$482.91		$528.5411	$528.55	$528.50	$528.50