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	$96.90	5.400%	$102.1326	$102.13	$102.15	$102.10
Purchase #2	$230.31	10.712%	$254.9808	$254.98	$255.00	$255.00
Purchase #3	$240.43	6.426%	$255.88	$255.88	$255.90	$255.90
Purchase #4	$54.60	8.628%	$59.3109	$59.31	$59.30	$59.30
Purchase #5	$191.32	5.153%	$201.1787	$201.18	$201.20	$201.20
Purchase #6	$60.71	9.403%	$66.4186	$66.42	$66.40	$66.40
Purchase #7	$106.97	4.303%	$111.5729	$111.57	$111.55	$111.60
7 purchase totals =	$981.24		$1,051.4745	$1,051.47	$1,051.50	$1,051.50