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	$233.69	3.542%	$241.9673	$241.97	$241.95	$242.00
Purchase #2	$132.82	6.481%	$141.4281	$141.43	$141.45	$141.40
Purchase #3	$107.76	11.383%	$120.0263	$120.03	$120.05	$120.00
Purchase #4	$99.92	11.309%	$111.22	$111.22	$111.20	$111.20
Purchase #5	$68.76	5.442%	$72.5019	$72.50	$72.50	$72.50
Purchase #6	$147.56	12.230%	$165.6066	$165.61	$165.60	$165.60
Purchase #7	$126.32	5.335%	$133.0592	$133.06	$133.05	$133.10
7 purchase totals =	$916.83		$985.8094	$985.82	$985.80	$985.80