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	$123.69	6.260%	$131.433	$131.43	$131.45	$131.40
Purchase #2	$238.78	11.487%	$266.2087	$266.21	$266.20	$266.20
Purchase #3	$122.90	7.861%	$132.5612	$132.56	$132.55	$132.60
Purchase #4	$247.88	7.852%	$267.3435	$267.34	$267.35	$267.30
Purchase #5	$78.58	4.659%	$82.241	$82.24	$82.25	$82.20
Purchase #6	$59.83	9.131%	$65.2931	$65.29	$65.30	$65.30
Purchase #7	$63.93	8.311%	$69.2432	$69.24	$69.25	$69.20
7 purchase totals =	$935.59		$1,014.3237	$1,014.31	$1,014.35	$1,014.20