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	$129.90	5.868%	$137.5225	$137.52	$137.50	$137.50
Purchase #2	$114.46	11.348%	$127.4489	$127.45	$127.45	$127.40
Purchase #3	$134.59	4.867%	$141.1405	$141.14	$141.15	$141.10
Purchase #4	$23.27	11.166%	$25.8683	$25.87	$25.85	$25.90
Purchase #5	$27.66	4.350%	$28.8632	$28.86	$28.85	$28.90
Purchase #6	$38.58	8.691%	$41.933	$41.93	$41.95	$41.90
Purchase #7	$13.42	8.223%	$14.5235	$14.52	$14.50	$14.50
7 purchase totals =	$481.88		$517.2999	$517.29	$517.25	$517.20