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	$43.25	4.451%	$45.1751	$45.18	$45.20	$45.20
Purchase #2	$35.90	8.332%	$38.8912	$38.89	$38.90	$38.90
Purchase #3	$97.87	3.163%	$100.9656	$100.97	$100.95	$101.00
Purchase #4	$172.77	6.819%	$184.5512	$184.55	$184.55	$184.60
Purchase #5	$245.45	11.374%	$273.3675	$273.37	$273.35	$273.40
Purchase #6	$223.60	6.804%	$238.8137	$238.81	$238.80	$238.80
Purchase #7	$198.70	9.497%	$217.5705	$217.57	$217.55	$217.60
7 purchase totals =	$1,017.54		$1,099.3348	$1,099.34	$1,099.30	$1,099.50