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	$161.77	13.705%	$183.9406	$183.94	$183.95	$183.90
Purchase #2	$154.86	11.384%	$172.4893	$172.49	$172.50	$172.50
Purchase #3	$208.68	5.163%	$219.4541	$219.45	$219.45	$219.50
Purchase #4	$54.80	4.568%	$57.3033	$57.30	$57.30	$57.30
Purchase #5	$34.35	3.450%	$35.5351	$35.54	$35.55	$35.50
Purchase #6	$52.26	7.715%	$56.2919	$56.29	$56.30	$56.30
Purchase #7	$47.88	13.527%	$54.3567	$54.36	$54.35	$54.40
7 purchase totals =	$714.60		$779.3710	$779.37	$779.40	$779.40