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	$11.42	6.852%	$12.2025	$12.20	$12.20	$12.20
Purchase #2	$155.94	7.439%	$167.5404	$167.54	$167.55	$167.50
Purchase #3	$134.40	6.813%	$143.5567	$143.56	$143.55	$143.60
Purchase #4	$80.60	7.488%	$86.6353	$86.64	$86.65	$86.60
Purchase #5	$113.36	12.361%	$127.3724	$127.37	$127.35	$127.40
Purchase #6	$104.26	13.845%	$118.6948	$118.69	$118.70	$118.70
Purchase #7	$171.53	8.191%	$185.58	$185.58	$185.60	$185.60
7 purchase totals =	$771.51		$841.5821	$841.58	$841.60	$841.60