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	$240.67	5.222%	$253.2378	$253.24	$253.25	$253.20
Purchase #2	$31.50	9.182%	$34.3923	$34.39	$34.40	$34.40
Purchase #3	$134.91	6.241%	$143.3297	$143.33	$143.35	$143.30
Purchase #4	$79.98	13.165%	$90.5094	$90.51	$90.50	$90.50
Purchase #5	$132.58	7.807%	$142.9305	$142.93	$142.95	$142.90
Purchase #6	$64.87	7.540%	$69.7612	$69.76	$69.75	$69.80
Purchase #7	$176.84	3.160%	$182.4281	$182.43	$182.45	$182.40
7 purchase totals =	$861.35		$916.5890	$916.59	$916.65	$916.50