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	$113.83	3.290%	$117.575	$117.58	$117.60	$117.60
Purchase #2	$84.94	7.861%	$91.6171	$91.62	$91.60	$91.60
Purchase #3	$185.52	7.509%	$199.4507	$199.45	$199.45	$199.50
Purchase #4	$200.57	10.712%	$222.0551	$222.06	$222.05	$222.10
Purchase #5	$114.98	11.118%	$127.7635	$127.76	$127.75	$127.80
Purchase #6	$60.62	13.675%	$68.9098	$68.91	$68.90	$68.90
Purchase #7	$153.79	6.722%	$164.1278	$164.13	$164.15	$164.10
7 purchase totals =	$914.25		$991.4990	$991.51	$991.50	$991.60