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	$100.46	12.795%	$113.3139	$113.31	$113.30	$113.30
Purchase #2	$216.84	10.137%	$238.8211	$238.82	$238.80	$238.80
Purchase #3	$87.86	5.521%	$92.7108	$92.71	$92.70	$92.70
Purchase #4	$199.56	5.191%	$209.9192	$209.92	$209.90	$209.90
Purchase #5	$148.89	12.177%	$167.0203	$167.02	$167.00	$167.00
Purchase #6	$214.97	11.108%	$238.8489	$238.85	$238.85	$238.80
Purchase #7	$185.52	8.594%	$201.4636	$201.46	$201.45	$201.50
7 purchase totals =	$1,154.10		$1,262.0978	$1,262.09	$1,262.00	$1,262.00