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	$74.80	5.481%	$78.8998	$78.90	$78.90	$78.90
Purchase #2	$164.90	4.849%	$172.896	$172.90	$172.90	$172.90
Purchase #3	$118.33	12.456%	$133.0692	$133.07	$133.05	$133.10
Purchase #4	$27.85	9.293%	$30.4381	$30.44	$30.45	$30.40
Purchase #5	$124.34	6.370%	$132.2605	$132.26	$132.25	$132.30
Purchase #6	$202.71	13.781%	$230.6455	$230.65	$230.65	$230.60
Purchase #7	$54.59	3.216%	$56.3456	$56.35	$56.35	$56.30
7 purchase totals =	$767.52		$834.5547	$834.57	$834.55	$834.50