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	$117.35	12.135%	$131.5904	$131.59	$131.60	$131.60
Purchase #2	$122.97	9.241%	$134.3337	$134.33	$134.35	$134.30
Purchase #3	$57.64	7.417%	$61.9152	$61.92	$61.90	$61.90
Purchase #4	$101.50	13.834%	$115.5415	$115.54	$115.55	$115.50
Purchase #5	$239.55	4.396%	$250.0806	$250.08	$250.10	$250.10
Purchase #6	$25.25	12.733%	$28.4651	$28.47	$28.45	$28.50
Purchase #7	$164.52	5.839%	$174.1263	$174.13	$174.15	$174.10
7 purchase totals =	$828.78		$896.0528	$896.06	$896.10	$896.00