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	$118.84	13.250%	$134.5863	$134.59	$134.60	$134.60
Purchase #2	$155.26	8.749%	$168.8437	$168.84	$168.85	$168.80
Purchase #3	$215.34	5.467%	$227.1126	$227.11	$227.10	$227.10
Purchase #4	$96.49	11.848%	$107.9221	$107.92	$107.90	$107.90
Purchase #5	$41.73	11.685%	$46.6062	$46.61	$46.60	$46.60
Purchase #6	$104.86	6.748%	$111.936	$111.94	$111.95	$111.90
Purchase #7	$203.56	8.607%	$221.0804	$221.08	$221.10	$221.10
7 purchase totals =	$936.08		$1,018.0873	$1,018.09	$1,018.10	$1,018.00