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	$139.53	4.347%	$145.5954	$145.60	$145.60	$145.60
Purchase #2	$40.67	4.459%	$42.4835	$42.48	$42.50	$42.50
Purchase #3	$169.76	13.544%	$192.7523	$192.75	$192.75	$192.80
Purchase #4	$121.43	13.849%	$138.2468	$138.25	$138.25	$138.20
Purchase #5	$240.47	3.613%	$249.1582	$249.16	$249.15	$249.20
Purchase #6	$103.99	12.117%	$116.5905	$116.59	$116.60	$116.60
Purchase #7	$96.30	9.784%	$105.722	$105.72	$105.70	$105.70
7 purchase totals =	$912.15		$990.5487	$990.55	$990.55	$990.60