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	$11.70	7.545%	$12.5828	$12.58	$12.60	$12.60
Purchase #2	$238.88	4.779%	$250.2961	$250.30	$250.30	$250.30
Purchase #3	$97.72	10.643%	$108.1203	$108.12	$108.10	$108.10
Purchase #4	$134.35	13.354%	$152.2911	$152.29	$152.30	$152.30
Purchase #5	$248.87	9.283%	$271.9726	$271.97	$271.95	$272.00
Purchase #6	$162.60	3.567%	$168.3999	$168.40	$168.40	$168.40
Purchase #7	$173.83	12.794%	$196.0698	$196.07	$196.05	$196.10
7 purchase totals =	$1,067.95		$1,159.7326	$1,159.73	$1,159.70	$1,159.80