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	$233.67	8.438%	$253.3871	$253.39	$253.40	$253.40
Purchase #2	$110.80	4.529%	$115.8181	$115.82	$115.80	$115.80
Purchase #3	$100.87	10.783%	$111.7468	$111.75	$111.75	$111.70
Purchase #4	$127.72	8.829%	$138.9964	$139.00	$139.00	$139.00
Purchase #5	$174.59	4.217%	$181.9525	$181.95	$181.95	$182.00
Purchase #6	$139.78	5.115%	$146.9297	$146.93	$146.95	$146.90
Purchase #7	$27.37	7.521%	$29.4285	$29.43	$29.45	$29.40
7 purchase totals =	$914.80		$978.2591	$978.27	$978.30	$978.20