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	$238.63	8.172%	$258.1308	$258.13	$258.15	$258.10
Purchase #2	$50.93	8.562%	$55.2906	$55.29	$55.30	$55.30
Purchase #3	$250.25	13.520%	$284.0838	$284.08	$284.10	$284.10
Purchase #4	$67.98	13.623%	$77.2409	$77.24	$77.25	$77.20
Purchase #5	$133.40	6.808%	$142.4819	$142.48	$142.50	$142.50
Purchase #6	$62.53	6.493%	$66.5901	$66.59	$66.60	$66.60
Purchase #7	$164.78	9.393%	$180.2578	$180.26	$180.25	$180.30
7 purchase totals =	$968.50		$1,064.0759	$1,064.07	$1,064.15	$1,064.10