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	$28.27	11.410%	$31.4956	$31.50	$31.50	$31.50
Purchase #2	$54.61	8.544%	$59.2759	$59.28	$59.30	$59.30
Purchase #3	$229.98	13.325%	$260.6248	$260.62	$260.60	$260.60
Purchase #4	$113.59	10.620%	$125.6533	$125.65	$125.65	$125.70
Purchase #5	$33.49	5.254%	$35.2496	$35.25	$35.25	$35.20
Purchase #6	$139.83	9.490%	$153.0999	$153.10	$153.10	$153.10
Purchase #7	$151.41	4.752%	$158.605	$158.61	$158.60	$158.60
7 purchase totals =	$751.18		$824.0041	$824.01	$824.00	$824.00