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	$18.32	11.786%	$20.4792	$20.48	$20.50	$20.50
Purchase #2	$236.90	10.233%	$261.142	$261.14	$261.15	$261.10
Purchase #3	$29.59	8.539%	$32.1167	$32.12	$32.10	$32.10
Purchase #4	$89.72	4.783%	$94.0113	$94.01	$94.00	$94.00
Purchase #5	$40.42	8.638%	$43.9115	$43.91	$43.90	$43.90
Purchase #6	$185.30	9.514%	$202.9294	$202.93	$202.95	$202.90
Purchase #7	$25.92	7.426%	$27.8448	$27.84	$27.85	$27.80
7 purchase totals =	$626.17		$682.4349	$682.43	$682.45	$682.30