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	$249.51	9.121%	$272.2678	$272.27	$272.25	$272.30
Purchase #2	$145.91	6.321%	$155.133	$155.13	$155.15	$155.10
Purchase #3	$107.28	7.658%	$115.4955	$115.50	$115.50	$115.50
Purchase #4	$134.93	8.582%	$146.5097	$146.51	$146.50	$146.50
Purchase #5	$51.71	3.468%	$53.5033	$53.50	$53.50	$53.50
Purchase #6	$42.61	4.442%	$44.5027	$44.50	$44.50	$44.50
Purchase #7	$92.55	10.785%	$102.5315	$102.53	$102.55	$102.50
7 purchase totals =	$824.50		$889.9435	$889.94	$889.95	$889.90