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	$76.64	7.387%	$82.3014	$82.30	$82.30	$82.30
Purchase #2	$248.95	3.760%	$258.3105	$258.31	$258.30	$258.30
Purchase #3	$54.38	9.249%	$59.4096	$59.41	$59.40	$59.40
Purchase #4	$47.37	8.605%	$51.4462	$51.45	$51.45	$51.40
Purchase #5	$187.49	7.639%	$201.8124	$201.81	$201.80	$201.80
Purchase #6	$41.46	9.758%	$45.5057	$45.51	$45.50	$45.50
Purchase #7	$95.65	5.823%	$101.2197	$101.22	$101.20	$101.20
7 purchase totals =	$751.94		$800.0055	$800.01	$799.95	$799.90