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	$244.31	4.464%	$255.216	$255.22	$255.20	$255.20
Purchase #2	$160.63	5.473%	$169.4213	$169.42	$169.40	$169.40
Purchase #3	$126.26	8.783%	$137.3494	$137.35	$137.35	$137.30
Purchase #4	$181.43	12.349%	$203.8348	$203.83	$203.85	$203.80
Purchase #5	$38.84	4.438%	$40.5637	$40.56	$40.55	$40.60
Purchase #6	$109.53	12.552%	$123.2782	$123.28	$123.30	$123.30
Purchase #7	$131.70	10.672%	$145.755	$145.76	$145.75	$145.80
7 purchase totals =	$992.70		$1,075.4184	$1,075.42	$1,075.40	$1,075.40