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	$122.72	6.405%	$130.5802	$130.58	$130.60	$130.60
Purchase #2	$80.74	8.627%	$87.7054	$87.71	$87.70	$87.70
Purchase #3	$40.87	5.590%	$43.1546	$43.15	$43.15	$43.20
Purchase #4	$81.88	11.756%	$91.5058	$91.51	$91.50	$91.50
Purchase #5	$51.30	5.352%	$54.0456	$54.05	$54.05	$54.00
Purchase #6	$136.94	6.322%	$145.5973	$145.60	$145.60	$145.60
Purchase #7	$38.35	6.441%	$40.8201	$40.82	$40.80	$40.80
7 purchase totals =	$552.80		$593.4090	$593.42	$593.40	$593.40