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	$49.65	9.801%	$54.5162	$54.52	$54.50	$54.50
Purchase #2	$217.52	7.779%	$234.4409	$234.44	$234.45	$234.40
Purchase #3	$34.90	11.313%	$38.8482	$38.85	$38.85	$38.80
Purchase #4	$50.56	7.677%	$54.4415	$54.44	$54.45	$54.40
Purchase #5	$146.98	9.213%	$160.5213	$160.52	$160.50	$160.50
Purchase #6	$49.70	13.657%	$56.4875	$56.49	$56.50	$56.50
Purchase #7	$109.55	5.140%	$115.1809	$115.18	$115.20	$115.20
7 purchase totals =	$658.86		$714.4365	$714.44	$714.45	$714.30