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	$239.99	11.810%	$268.3328	$268.33	$268.35	$268.30
Purchase #2	$96.35	10.733%	$106.6912	$106.69	$106.70	$106.70
Purchase #3	$116.91	5.527%	$123.3716	$123.37	$123.35	$123.40
Purchase #4	$172.60	10.226%	$190.2501	$190.25	$190.25	$190.30
Purchase #5	$74.39	11.475%	$82.9263	$82.93	$82.95	$82.90
Purchase #6	$176.73	12.773%	$199.3037	$199.30	$199.30	$199.30
Purchase #7	$66.67	7.639%	$71.7629	$71.76	$71.75	$71.80
7 purchase totals =	$943.64		$1,042.6386	$1,042.63	$1,042.65	$1,042.70