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	$131.51	5.253%	$138.4182	$138.42	$138.40	$138.40
Purchase #2	$96.58	4.149%	$100.5871	$100.59	$100.60	$100.60
Purchase #3	$91.70	9.439%	$100.3556	$100.36	$100.35	$100.40
Purchase #4	$80.56	10.523%	$89.0373	$89.04	$89.05	$89.00
Purchase #5	$234.85	8.611%	$255.0729	$255.07	$255.05	$255.10
Purchase #6	$58.37	3.437%	$60.3762	$60.38	$60.40	$60.40
Purchase #7	$110.74	9.601%	$121.3721	$121.37	$121.35	$121.40
7 purchase totals =	$804.31		$865.2194	$865.23	$865.20	$865.30