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	$129.27	4.139%	$134.6205	$134.62	$134.60	$134.60
Purchase #2	$58.83	11.144%	$65.386	$65.39	$65.40	$65.40
Purchase #3	$231.99	10.285%	$255.8502	$255.85	$255.85	$255.90
Purchase #4	$25.53	9.601%	$27.9811	$27.98	$28.00	$28.00
Purchase #5	$71.82	11.652%	$80.1885	$80.19	$80.20	$80.20
Purchase #6	$248.68	5.319%	$261.9073	$261.91	$261.90	$261.90
Purchase #7	$164.70	7.363%	$176.8269	$176.83	$176.85	$176.80
7 purchase totals =	$930.82		$1,002.7605	$1,002.77	$1,002.80	$1,002.80