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	$166.42	13.507%	$188.8983	$188.90	$188.90	$188.90
Purchase #2	$112.60	5.693%	$119.0103	$119.01	$119.00	$119.00
Purchase #3	$99.61	13.778%	$113.3343	$113.33	$113.35	$113.30
Purchase #4	$126.43	5.108%	$132.888	$132.89	$132.90	$132.90
Purchase #5	$153.61	13.119%	$173.7621	$173.76	$173.75	$173.80
Purchase #6	$99.48	5.477%	$104.9285	$104.93	$104.95	$104.90
Purchase #7	$91.68	3.103%	$94.5248	$94.52	$94.50	$94.50
7 purchase totals =	$849.83		$927.3463	$927.34	$927.35	$927.30