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	$190.46	13.340%	$215.8674	$215.87	$215.85	$215.90
Purchase #2	$129.46	10.577%	$143.153	$143.15	$143.15	$143.20
Purchase #3	$207.81	10.636%	$229.9127	$229.91	$229.90	$229.90
Purchase #4	$133.82	12.141%	$150.0671	$150.07	$150.05	$150.10
Purchase #5	$144.77	10.331%	$159.7262	$159.73	$159.75	$159.70
Purchase #6	$28.79	12.760%	$32.4636	$32.46	$32.45	$32.50
Purchase #7	$35.77	12.448%	$40.2226	$40.22	$40.20	$40.20
7 purchase totals =	$870.88		$971.4126	$971.41	$971.35	$971.50