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	$39.64	4.123%	$41.2744	$41.27	$41.25	$41.30
Purchase #2	$125.25	10.872%	$138.8672	$138.87	$138.85	$138.90
Purchase #3	$19.84	7.536%	$21.3351	$21.34	$21.35	$21.30
Purchase #4	$85.94	3.815%	$89.2186	$89.22	$89.20	$89.20
Purchase #5	$31.57	8.557%	$34.2714	$34.27	$34.25	$34.30
Purchase #6	$151.70	13.558%	$172.2675	$172.27	$172.25	$172.30
Purchase #7	$62.63	6.461%	$66.6765	$66.68	$66.70	$66.70
7 purchase totals =	$516.57		$563.9107	$563.92	$563.85	$564.00