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	$45.81	3.729%	$47.5183	$47.52	$47.50	$47.50
Purchase #2	$52.35	7.450%	$56.2501	$56.25	$56.25	$56.30
Purchase #3	$227.91	4.431%	$238.0087	$238.01	$238.00	$238.00
Purchase #4	$108.61	7.418%	$116.6667	$116.67	$116.65	$116.70
Purchase #5	$98.28	13.167%	$111.2205	$111.22	$111.20	$111.20
Purchase #6	$197.96	11.474%	$220.6739	$220.67	$220.65	$220.70
Purchase #7	$102.45	8.848%	$111.5148	$111.51	$111.50	$111.50
7 purchase totals =	$833.37		$901.8530	$901.85	$901.75	$901.90