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	$248.41	5.300%	$261.5757	$261.58	$261.60	$261.60
Purchase #2	$106.51	8.570%	$115.6379	$115.64	$115.65	$115.60
Purchase #3	$121.41	10.436%	$134.0803	$134.08	$134.10	$134.10
Purchase #4	$115.78	10.157%	$127.5398	$127.54	$127.55	$127.50
Purchase #5	$57.63	3.371%	$59.5727	$59.57	$59.55	$59.60
Purchase #6	$27.39	3.140%	$28.25	$28.25	$28.25	$28.30
Purchase #7	$54.29	13.832%	$61.7994	$61.80	$61.80	$61.80
7 purchase totals =	$731.42		$788.4558	$788.46	$788.50	$788.50