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	$201.92	9.653%	$221.4113	$221.41	$221.40	$221.40
Purchase #2	$79.27	4.487%	$82.8268	$82.83	$82.85	$82.80
Purchase #3	$187.40	12.389%	$210.617	$210.62	$210.60	$210.60
Purchase #4	$128.98	5.748%	$136.3938	$136.39	$136.40	$136.40
Purchase #5	$203.87	7.668%	$219.5028	$219.50	$219.50	$219.50
Purchase #6	$152.56	13.337%	$172.9069	$172.91	$172.90	$172.90
Purchase #7	$158.85	9.446%	$173.855	$173.86	$173.85	$173.90
7 purchase totals =	$1,112.85		$1,217.5136	$1,217.52	$1,217.50	$1,217.50