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	$114.30	11.304%	$127.2205	$127.22	$127.20	$127.20
Purchase #2	$12.53	3.598%	$12.9808	$12.98	$13.00	$13.00
Purchase #3	$175.49	5.342%	$184.8647	$184.86	$184.85	$184.90
Purchase #4	$70.40	13.691%	$80.0385	$80.04	$80.05	$80.00
Purchase #5	$53.86	7.390%	$57.8403	$57.84	$57.85	$57.80
Purchase #6	$100.46	8.522%	$109.0212	$109.02	$109.00	$109.00
Purchase #7	$93.45	9.565%	$102.3885	$102.39	$102.40	$102.40
7 purchase totals =	$620.49		$674.3545	$674.35	$674.35	$674.30