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	$72.43	13.271%	$82.0422	$82.04	$82.05	$82.00
Purchase #2	$231.82	13.212%	$262.4481	$262.45	$262.45	$262.40
Purchase #3	$169.91	12.453%	$191.0689	$191.07	$191.05	$191.10
Purchase #4	$123.68	6.260%	$131.4224	$131.42	$131.40	$131.40
Purchase #5	$45.77	12.161%	$51.3361	$51.34	$51.35	$51.30
Purchase #6	$204.71	7.587%	$220.2413	$220.24	$220.25	$220.20
Purchase #7	$221.45	8.439%	$240.1382	$240.14	$240.15	$240.10
7 purchase totals =	$1,069.77		$1,178.6972	$1,178.70	$1,178.70	$1,178.50