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	$115.54	10.380%	$127.5331	$127.53	$127.55	$127.50
Purchase #2	$205.84	8.671%	$223.6884	$223.69	$223.70	$223.70
Purchase #3	$10.68	4.657%	$11.1774	$11.18	$11.20	$11.20
Purchase #4	$169.60	5.269%	$178.5362	$178.54	$178.55	$178.50
Purchase #5	$92.67	13.332%	$105.0248	$105.02	$105.00	$105.00
Purchase #6	$113.37	6.289%	$120.4998	$120.50	$120.50	$120.50
Purchase #7	$27.27	9.387%	$29.8298	$29.83	$29.85	$29.80
7 purchase totals =	$734.97		$796.2895	$796.29	$796.35	$796.20