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	$50.96	9.205%	$55.6509	$55.65	$55.65	$55.70
Purchase #2	$75.29	3.671%	$78.0539	$78.05	$78.05	$78.10
Purchase #3	$126.98	8.309%	$137.5308	$137.53	$137.55	$137.50
Purchase #4	$107.61	3.481%	$111.3559	$111.36	$111.35	$111.40
Purchase #5	$89.83	12.794%	$101.3229	$101.32	$101.30	$101.30
Purchase #6	$133.62	12.522%	$150.3519	$150.35	$150.35	$150.40
Purchase #7	$136.27	5.583%	$143.878	$143.88	$143.90	$143.90
7 purchase totals =	$720.56		$778.1443	$778.14	$778.15	$778.30