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	$25.75	9.866%	$28.2905	$28.29	$28.30	$28.30
Purchase #2	$49.89	9.395%	$54.5772	$54.58	$54.60	$54.60
Purchase #3	$36.43	6.457%	$38.7823	$38.78	$38.80	$38.80
Purchase #4	$60.42	4.580%	$63.1872	$63.19	$63.20	$63.20
Purchase #5	$45.52	4.579%	$47.6044	$47.60	$47.60	$47.60
Purchase #6	$36.43	13.805%	$41.4592	$41.46	$41.45	$41.50
Purchase #7	$57.44	7.219%	$61.5866	$61.59	$61.60	$61.60
7 purchase totals =	$311.88		$335.4874	$335.49	$335.55	$335.60