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	$47.77	13.460%	$54.1998	$54.20	$54.20	$54.20
Purchase #2	$51.52	5.290%	$54.2454	$54.25	$54.25	$54.20
Purchase #3	$166.28	7.511%	$178.7693	$178.77	$178.75	$178.80
Purchase #4	$77.54	3.708%	$80.4152	$80.42	$80.40	$80.40
Purchase #5	$243.64	8.134%	$263.4577	$263.46	$263.45	$263.50
Purchase #6	$175.65	13.463%	$199.2978	$199.30	$199.30	$199.30
Purchase #7	$228.29	12.270%	$256.3012	$256.30	$256.30	$256.30
7 purchase totals =	$990.69		$1,086.6864	$1,086.70	$1,086.65	$1,086.70