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	$231.78	12.824%	$261.5035	$261.50	$261.50	$261.50
Purchase #2	$114.28	6.564%	$121.7813	$121.78	$121.80	$121.80
Purchase #3	$120.58	5.748%	$127.5109	$127.51	$127.50	$127.50
Purchase #4	$112.86	12.419%	$126.8761	$126.88	$126.90	$126.90
Purchase #5	$175.51	3.582%	$181.7968	$181.80	$181.80	$181.80
Purchase #6	$130.50	13.815%	$148.5286	$148.53	$148.55	$148.50
Purchase #7	$25.93	11.526%	$28.9187	$28.92	$28.90	$28.90
7 purchase totals =	$911.44		$996.9159	$996.92	$996.95	$996.90