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	$227.66	9.815%	$250.0048	$250.00	$250.00	$250.00
Purchase #2	$245.43	4.641%	$256.8204	$256.82	$256.80	$256.80
Purchase #3	$85.54	5.764%	$90.4705	$90.47	$90.45	$90.50
Purchase #4	$37.26	11.587%	$41.5773	$41.58	$41.60	$41.60
Purchase #5	$50.83	7.128%	$54.4532	$54.45	$54.45	$54.50
Purchase #6	$18.69	13.513%	$21.2156	$21.22	$21.20	$21.20
Purchase #7	$43.80	9.188%	$47.8243	$47.82	$47.80	$47.80
7 purchase totals =	$709.21		$762.3661	$762.36	$762.30	$762.40