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	$226.93	12.469%	$255.2259	$255.23	$255.25	$255.20
Purchase #2	$155.84	7.223%	$167.0963	$167.10	$167.10	$167.10
Purchase #3	$140.40	11.443%	$156.466	$156.47	$156.45	$156.50
Purchase #4	$50.69	9.348%	$55.4285	$55.43	$55.45	$55.40
Purchase #5	$15.92	11.393%	$17.7338	$17.73	$17.75	$17.70
Purchase #6	$90.78	13.188%	$102.7521	$102.75	$102.75	$102.80
Purchase #7	$85.46	7.821%	$92.1438	$92.14	$92.15	$92.10
7 purchase totals =	$766.02		$846.8464	$846.85	$846.90	$846.80