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	$56.97	3.589%	$59.0147	$59.01	$59.00	$59.00
Purchase #2	$248.96	10.835%	$275.9348	$275.93	$275.95	$275.90
Purchase #3	$82.36	6.370%	$87.6063	$87.61	$87.60	$87.60
Purchase #4	$113.68	8.773%	$123.6531	$123.65	$123.65	$123.70
Purchase #5	$243.27	4.725%	$254.7645	$254.76	$254.75	$254.80
Purchase #6	$155.65	9.225%	$170.0087	$170.01	$170.00	$170.00
Purchase #7	$245.83	13.777%	$279.698	$279.70	$279.70	$279.70
7 purchase totals =	$1,146.72		$1,250.6801	$1,250.67	$1,250.65	$1,250.70