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	$21.26	7.681%	$22.893	$22.89	$22.90	$22.90
Purchase #2	$154.84	7.783%	$166.8912	$166.89	$166.90	$166.90
Purchase #3	$198.78	3.195%	$205.131	$205.13	$205.15	$205.10
Purchase #4	$184.83	5.760%	$195.4762	$195.48	$195.50	$195.50
Purchase #5	$103.38	5.453%	$109.0173	$109.02	$109.00	$109.00
Purchase #6	$127.96	12.426%	$143.8603	$143.86	$143.85	$143.90
Purchase #7	$31.71	10.120%	$34.9191	$34.92	$34.90	$34.90
7 purchase totals =	$822.76		$878.1881	$878.19	$878.20	$878.20