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	$37.66	7.477%	$40.4758	$40.48	$40.50	$40.50
Purchase #2	$112.83	12.138%	$126.5253	$126.53	$126.55	$126.50
Purchase #3	$242.93	3.359%	$251.09	$251.09	$251.10	$251.10
Purchase #4	$212.54	8.328%	$230.2403	$230.24	$230.25	$230.20
Purchase #5	$247.56	4.372%	$258.3833	$258.38	$258.40	$258.40
Purchase #6	$109.82	12.414%	$123.4531	$123.45	$123.45	$123.50
Purchase #7	$45.66	10.601%	$50.5004	$50.50	$50.50	$50.50
7 purchase totals =	$1,009.00		$1,080.6682	$1,080.67	$1,080.75	$1,080.70