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	$45.71	3.823%	$47.4575	$47.46	$47.45	$47.50
Purchase #2	$244.81	4.694%	$256.3014	$256.30	$256.30	$256.30
Purchase #3	$217.75	7.297%	$233.6392	$233.64	$233.65	$233.60
Purchase #4	$18.91	12.351%	$21.2456	$21.25	$21.25	$21.20
Purchase #5	$94.57	9.795%	$103.8331	$103.83	$103.85	$103.80
Purchase #6	$176.82	4.568%	$184.8971	$184.90	$184.90	$184.90
Purchase #7	$223.86	3.220%	$231.0683	$231.07	$231.05	$231.10
7 purchase totals =	$1,022.43		$1,078.4422	$1,078.45	$1,078.45	$1,078.40