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	$63.93	13.406%	$72.5005	$72.50	$72.50	$72.50
Purchase #2	$226.96	10.402%	$250.5684	$250.57	$250.55	$250.60
Purchase #3	$39.86	11.551%	$44.4642	$44.46	$44.45	$44.50
Purchase #4	$164.81	8.136%	$178.2189	$178.22	$178.20	$178.20
Purchase #5	$181.35	6.267%	$192.7152	$192.72	$192.70	$192.70
Purchase #6	$115.80	9.776%	$127.1206	$127.12	$127.10	$127.10
Purchase #7	$36.55	13.467%	$41.4722	$41.47	$41.45	$41.50
7 purchase totals =	$829.26		$907.0600	$907.06	$906.95	$907.10