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	$242.36	12.590%	$272.8731	$272.87	$272.85	$272.90
Purchase #2	$92.80	7.398%	$99.6653	$99.67	$99.65	$99.70
Purchase #3	$157.83	3.333%	$163.0905	$163.09	$163.10	$163.10
Purchase #4	$119.35	11.139%	$132.6444	$132.64	$132.65	$132.60
Purchase #5	$33.72	6.433%	$35.8892	$35.89	$35.90	$35.90
Purchase #6	$36.44	12.778%	$41.0963	$41.10	$41.10	$41.10
Purchase #7	$56.35	4.753%	$59.0283	$59.03	$59.05	$59.00
7 purchase totals =	$738.85		$804.2871	$804.29	$804.30	$804.30