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	$70.44	10.579%	$77.8918	$77.89	$77.90	$77.90
Purchase #2	$63.90	3.438%	$66.0969	$66.10	$66.10	$66.10
Purchase #3	$5.27	5.221%	$5.5451	$5.55	$5.55	$5.50
Purchase #4	$128.56	13.504%	$145.9207	$145.92	$145.90	$145.90
Purchase #5	$81.62	10.731%	$90.3786	$90.38	$90.40	$90.40
Purchase #6	$94.40	9.724%	$103.5795	$103.58	$103.60	$103.60
Purchase #7	$119.25	9.142%	$130.1518	$130.15	$130.15	$130.20
7 purchase totals =	$563.44		$619.5644	$619.57	$619.60	$619.60