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	$77.39	10.872%	$85.8038	$85.80	$85.80	$85.80
Purchase #2	$171.26	6.870%	$183.0256	$183.03	$183.05	$183.00
Purchase #3	$119.74	8.854%	$130.3418	$130.34	$130.35	$130.30
Purchase #4	$202.79	6.624%	$216.2228	$216.22	$216.20	$216.20
Purchase #5	$103.60	7.588%	$111.4612	$111.46	$111.45	$111.50
Purchase #6	$60.38	10.160%	$66.5146	$66.51	$66.50	$66.50
Purchase #7	$131.34	13.836%	$149.5122	$149.51	$149.50	$149.50
7 purchase totals =	$866.50		$942.8820	$942.87	$942.85	$942.80