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	$89.91	12.108%	$100.7963	$100.80	$100.80	$100.80
Purchase #2	$25.42	4.174%	$26.481	$26.48	$26.50	$26.50
Purchase #3	$10.99	6.868%	$11.7448	$11.74	$11.75	$11.70
Purchase #4	$73.92	10.699%	$81.8287	$81.83	$81.85	$81.80
Purchase #5	$19.94	6.277%	$21.1916	$21.19	$21.20	$21.20
Purchase #6	$188.29	4.288%	$196.3639	$196.36	$196.35	$196.40
Purchase #7	$66.47	9.286%	$72.6424	$72.64	$72.65	$72.60
7 purchase totals =	$474.94		$511.0487	$511.04	$511.10	$511.00