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	$215.78	12.413%	$242.5648	$242.56	$242.55	$242.60
Purchase #2	$68.50	12.133%	$76.8111	$76.81	$76.80	$76.80
Purchase #3	$41.39	5.182%	$43.5348	$43.53	$43.55	$43.50
Purchase #4	$21.83	4.873%	$22.8938	$22.89	$22.90	$22.90
Purchase #5	$209.91	10.113%	$231.1382	$231.14	$231.15	$231.10
Purchase #6	$43.34	6.153%	$46.0067	$46.01	$46.00	$46.00
Purchase #7	$37.94	9.826%	$41.668	$41.67	$41.65	$41.70
7 purchase totals =	$638.69		$704.6174	$704.61	$704.60	$704.60