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	$245.39	13.707%	$279.0256	$279.03	$279.05	$279.00
Purchase #2	$83.87	6.871%	$89.6327	$89.63	$89.65	$89.60
Purchase #3	$209.41	8.230%	$226.6444	$226.64	$226.65	$226.60
Purchase #4	$31.42	3.728%	$32.5913	$32.59	$32.60	$32.60
Purchase #5	$39.71	10.729%	$43.9705	$43.97	$43.95	$44.00
Purchase #6	$198.74	9.428%	$217.4772	$217.48	$217.50	$217.50
Purchase #7	$52.94	9.324%	$57.8761	$57.88	$57.90	$57.90
7 purchase totals =	$861.48		$947.2178	$947.22	$947.30	$947.20