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	$19.50	9.376%	$21.3283	$21.33	$21.35	$21.30
Purchase #2	$25.43	9.725%	$27.9031	$27.90	$27.90	$27.90
Purchase #3	$234.39	11.699%	$261.8113	$261.81	$261.80	$261.80
Purchase #4	$180.88	8.368%	$196.016	$196.02	$196.00	$196.00
Purchase #5	$177.47	7.486%	$190.7554	$190.76	$190.75	$190.80
Purchase #6	$104.25	4.622%	$109.0684	$109.07	$109.05	$109.10
Purchase #7	$193.25	13.755%	$219.8315	$219.83	$219.85	$219.80
7 purchase totals =	$935.17		$1,026.7140	$1,026.72	$1,026.70	$1,026.70