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	$232.41	6.509%	$247.5376	$247.54	$247.55	$247.50
Purchase #2	$54.90	11.310%	$61.1092	$61.11	$61.10	$61.10
Purchase #3	$129.32	12.250%	$145.1617	$145.16	$145.15	$145.20
Purchase #4	$57.58	9.727%	$63.1808	$63.18	$63.20	$63.20
Purchase #5	$177.92	3.308%	$183.8056	$183.81	$183.80	$183.80
Purchase #6	$124.74	12.120%	$139.8585	$139.86	$139.85	$139.90
Purchase #7	$104.59	6.858%	$111.7628	$111.76	$111.75	$111.80
7 purchase totals =	$881.46		$952.4162	$952.42	$952.40	$952.50