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	$11.31	12.774%	$12.7547	$12.75	$12.75	$12.80
Purchase #2	$75.37	10.638%	$83.3879	$83.39	$83.40	$83.40
Purchase #3	$104.99	6.390%	$111.6989	$111.70	$111.70	$111.70
Purchase #4	$136.65	5.469%	$144.1234	$144.12	$144.10	$144.10
Purchase #5	$69.53	4.302%	$72.5212	$72.52	$72.50	$72.50
Purchase #6	$70.97	10.373%	$78.3317	$78.33	$78.35	$78.30
Purchase #7	$162.60	4.763%	$170.3446	$170.34	$170.35	$170.30
7 purchase totals =	$631.42		$673.1624	$673.15	$673.15	$673.10