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	$250.61	13.589%	$284.6654	$284.67	$284.65	$284.70
Purchase #2	$48.64	10.847%	$53.916	$53.92	$53.90	$53.90
Purchase #3	$44.84	13.831%	$51.0418	$51.04	$51.05	$51.00
Purchase #4	$104.48	11.592%	$116.5913	$116.59	$116.60	$116.60
Purchase #5	$46.78	13.441%	$53.0677	$53.07	$53.05	$53.10
Purchase #6	$44.64	10.118%	$49.1567	$49.16	$49.15	$49.20
Purchase #7	$180.35	8.870%	$196.347	$196.35	$196.35	$196.30
7 purchase totals =	$720.34		$804.7859	$804.80	$804.75	$804.80