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	$105.36	4.306%	$109.8968	$109.90	$109.90	$109.90
Purchase #2	$144.82	12.554%	$163.0007	$163.00	$163.00	$163.00
Purchase #3	$71.66	11.859%	$80.1582	$80.16	$80.15	$80.20
Purchase #4	$72.38	10.314%	$79.8453	$79.85	$79.85	$79.80
Purchase #5	$52.91	12.727%	$59.6439	$59.64	$59.65	$59.60
Purchase #6	$117.91	4.867%	$123.6487	$123.65	$123.65	$123.60
Purchase #7	$96.41	7.388%	$103.5328	$103.53	$103.55	$103.50
7 purchase totals =	$661.45		$719.7264	$719.73	$719.75	$719.60