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	$7.59	9.642%	$8.3218	$8.32	$8.30	$8.30
Purchase #2	$131.64	9.832%	$144.5828	$144.58	$144.60	$144.60
Purchase #3	$226.87	12.292%	$254.7569	$254.76	$254.75	$254.80
Purchase #4	$31.60	5.748%	$33.4164	$33.42	$33.40	$33.40
Purchase #5	$107.44	3.329%	$111.0167	$111.02	$111.00	$111.00
Purchase #6	$232.27	13.634%	$263.9377	$263.94	$263.95	$263.90
Purchase #7	$84.40	6.825%	$90.1603	$90.16	$90.15	$90.20
7 purchase totals =	$821.81		$906.1926	$906.20	$906.15	$906.20