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	$208.29	4.584%	$217.838	$217.84	$217.85	$217.80
Purchase #2	$144.33	9.753%	$158.4065	$158.41	$158.40	$158.40
Purchase #3	$63.77	10.546%	$70.4952	$70.50	$70.50	$70.50
Purchase #4	$112.41	3.695%	$116.5635	$116.56	$116.55	$116.60
Purchase #5	$93.84	6.712%	$100.1385	$100.14	$100.15	$100.10
Purchase #6	$152.33	4.127%	$158.6167	$158.62	$158.60	$158.60
Purchase #7	$216.85	8.476%	$235.2302	$235.23	$235.25	$235.20
7 purchase totals =	$991.82		$1,057.2886	$1,057.30	$1,057.30	$1,057.20