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	$192.42	13.705%	$218.7912	$218.79	$218.80	$218.80
Purchase #2	$132.64	7.236%	$142.2378	$142.24	$142.25	$142.20
Purchase #3	$6.28	4.522%	$6.564	$6.56	$6.55	$6.60
Purchase #4	$238.61	7.222%	$255.8424	$255.84	$255.85	$255.80
Purchase #5	$112.45	13.408%	$127.5273	$127.53	$127.55	$127.50
Purchase #6	$197.88	9.653%	$216.9814	$216.98	$217.00	$217.00
Purchase #7	$100.63	6.769%	$107.4416	$107.44	$107.45	$107.40
7 purchase totals =	$980.91		$1,075.3857	$1,075.38	$1,075.45	$1,075.30