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	$129.90	12.457%	$146.0816	$146.08	$146.10	$146.10
Purchase #2	$48.51	8.365%	$52.5679	$52.57	$52.55	$52.60
Purchase #3	$17.82	5.706%	$18.8368	$18.84	$18.85	$18.80
Purchase #4	$230.53	10.416%	$254.542	$254.54	$254.55	$254.50
Purchase #5	$237.39	12.466%	$266.983	$266.98	$267.00	$267.00
Purchase #6	$112.43	13.430%	$127.5293	$127.53	$127.55	$127.50
Purchase #7	$98.94	6.564%	$105.4344	$105.43	$105.45	$105.40
7 purchase totals =	$875.52		$971.9750	$971.97	$972.05	$971.90