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	$232.80	10.345%	$256.8832	$256.88	$256.90	$256.90
Purchase #2	$94.63	10.561%	$104.6239	$104.62	$104.60	$104.60
Purchase #3	$85.59	10.675%	$94.7267	$94.73	$94.75	$94.70
Purchase #4	$196.33	4.782%	$205.7185	$205.72	$205.70	$205.70
Purchase #5	$76.35	4.337%	$79.6613	$79.66	$79.65	$79.70
Purchase #6	$83.50	3.509%	$86.43	$86.43	$86.45	$86.40
Purchase #7	$82.34	3.493%	$85.2161	$85.22	$85.20	$85.20
7 purchase totals =	$851.54		$913.2597	$913.26	$913.25	$913.20