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	$96.98	5.795%	$102.6	$102.60	$102.60	$102.60
Purchase #2	$107.91	3.144%	$111.3027	$111.30	$111.30	$111.30
Purchase #3	$67.30	4.787%	$70.5217	$70.52	$70.50	$70.50
Purchase #4	$215.29	11.553%	$240.1625	$240.16	$240.15	$240.20
Purchase #5	$46.97	6.278%	$49.9188	$49.92	$49.90	$49.90
Purchase #6	$203.40	12.386%	$228.5931	$228.59	$228.60	$228.60
Purchase #7	$77.84	11.141%	$86.5122	$86.51	$86.50	$86.50
7 purchase totals =	$815.69		$889.6110	$889.60	$889.55	$889.60