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	$69.52	12.329%	$78.0911	$78.09	$78.10	$78.10
Purchase #2	$77.32	8.829%	$84.1466	$84.15	$84.15	$84.10
Purchase #3	$245.37	9.861%	$269.5659	$269.57	$269.55	$269.60
Purchase #4	$48.92	4.648%	$51.1938	$51.19	$51.20	$51.20
Purchase #5	$183.38	9.410%	$200.6361	$200.64	$200.65	$200.60
Purchase #6	$7.37	13.281%	$8.3488	$8.35	$8.35	$8.30
Purchase #7	$107.96	3.338%	$111.5637	$111.56	$111.55	$111.60
7 purchase totals =	$739.84		$803.5460	$803.55	$803.55	$803.50