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	$84.52	6.536%	$90.0442	$90.04	$90.05	$90.00
Purchase #2	$224.52	6.166%	$238.3639	$238.36	$238.35	$238.40
Purchase #3	$162.67	3.179%	$167.8413	$167.84	$167.85	$167.80
Purchase #4	$97.60	9.710%	$107.077	$107.08	$107.10	$107.10
Purchase #5	$176.76	3.254%	$182.5118	$182.51	$182.50	$182.50
Purchase #6	$246.97	9.758%	$271.0693	$271.07	$271.05	$271.10
Purchase #7	$35.31	11.365%	$39.323	$39.32	$39.30	$39.30
7 purchase totals =	$1,028.35		$1,096.2305	$1,096.22	$1,096.20	$1,096.20