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	$129.41	9.859%	$142.1685	$142.17	$142.15	$142.20
Purchase #2	$36.83	5.756%	$38.9499	$38.95	$38.95	$38.90
Purchase #3	$83.27	7.866%	$89.82	$89.82	$89.80	$89.80
Purchase #4	$133.76	8.149%	$144.6601	$144.66	$144.65	$144.70
Purchase #5	$38.71	11.509%	$43.1651	$43.17	$43.15	$43.20
Purchase #6	$236.27	12.146%	$264.9674	$264.97	$264.95	$265.00
Purchase #7	$15.68	9.748%	$17.2085	$17.21	$17.20	$17.20
7 purchase totals =	$673.93		$740.9395	$740.95	$740.85	$741.00