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	$129.32	5.292%	$136.1636	$136.16	$136.15	$136.20
Purchase #2	$73.27	12.577%	$82.4852	$82.49	$82.50	$82.50
Purchase #3	$192.25	9.805%	$211.1001	$211.10	$211.10	$211.10
Purchase #4	$95.69	3.168%	$98.7215	$98.72	$98.70	$98.70
Purchase #5	$107.80	3.114%	$111.1569	$111.16	$111.15	$111.20
Purchase #6	$153.93	5.462%	$162.3377	$162.34	$162.35	$162.30
Purchase #7	$175.71	8.628%	$190.8703	$190.87	$190.85	$190.90
7 purchase totals =	$927.97		$992.8353	$992.84	$992.80	$992.90