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	$219.93	13.713%	$250.089	$250.09	$250.10	$250.10
Purchase #2	$246.58	7.566%	$265.2362	$265.24	$265.25	$265.20
Purchase #3	$37.94	10.711%	$42.0038	$42.00	$42.00	$42.00
Purchase #4	$30.47	7.130%	$32.6425	$32.64	$32.65	$32.60
Purchase #5	$127.66	12.413%	$143.5064	$143.51	$143.50	$143.50
Purchase #6	$117.60	11.434%	$131.0464	$131.05	$131.05	$131.00
Purchase #7	$164.70	8.572%	$178.8181	$178.82	$178.80	$178.80
7 purchase totals =	$944.88		$1,043.3424	$1,043.35	$1,043.35	$1,043.20