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	$109.31	10.191%	$120.4498	$120.45	$120.45	$120.40
Purchase #2	$178.31	12.287%	$200.2189	$200.22	$200.20	$200.20
Purchase #3	$100.50	12.262%	$112.8233	$112.82	$112.80	$112.80
Purchase #4	$15.53	5.810%	$16.4323	$16.43	$16.45	$16.40
Purchase #5	$36.41	6.499%	$38.7763	$38.78	$38.80	$38.80
Purchase #6	$166.47	10.280%	$183.5831	$183.58	$183.60	$183.60
Purchase #7	$130.64	13.619%	$148.4319	$148.43	$148.45	$148.40
7 purchase totals =	$737.17		$820.7156	$820.71	$820.75	$820.60