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	$43.60	10.258%	$48.0725	$48.07	$48.05	$48.10
Purchase #2	$80.64	13.370%	$91.4216	$91.42	$91.40	$91.40
Purchase #3	$102.46	3.710%	$106.2613	$106.26	$106.25	$106.30
Purchase #4	$176.78	13.410%	$200.4862	$200.49	$200.50	$200.50
Purchase #5	$42.35	12.845%	$47.7899	$47.79	$47.80	$47.80
Purchase #6	$36.42	11.227%	$40.5089	$40.51	$40.50	$40.50
Purchase #7	$12.30	4.683%	$12.876	$12.88	$12.90	$12.90
7 purchase totals =	$494.55		$547.4164	$547.42	$547.40	$547.50