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	$99.61	13.716%	$113.2725	$113.27	$113.25	$113.30
Purchase #2	$56.66	9.838%	$62.2342	$62.23	$62.25	$62.20
Purchase #3	$139.97	13.872%	$159.3866	$159.39	$159.40	$159.40
Purchase #4	$79.41	4.309%	$82.8318	$82.83	$82.85	$82.80
Purchase #5	$89.83	8.277%	$97.2652	$97.27	$97.25	$97.30
Purchase #6	$217.88	7.542%	$234.3125	$234.31	$234.30	$234.30
Purchase #7	$242.45	6.381%	$257.9207	$257.92	$257.90	$257.90
7 purchase totals =	$925.81		$1,007.2235	$1,007.22	$1,007.20	$1,007.20