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	$115.53	12.584%	$130.0683	$130.07	$130.05	$130.10
Purchase #2	$124.66	5.290%	$131.2545	$131.25	$131.25	$131.30
Purchase #3	$107.37	6.230%	$114.0592	$114.06	$114.05	$114.10
Purchase #4	$164.72	9.740%	$180.7637	$180.76	$180.75	$180.80
Purchase #5	$17.74	3.195%	$18.3068	$18.31	$18.30	$18.30
Purchase #6	$14.45	6.365%	$15.3697	$15.37	$15.35	$15.40
Purchase #7	$236.42	5.745%	$250.0023	$250.00	$250.00	$250.00
7 purchase totals =	$780.89		$839.8245	$839.82	$839.75	$840.00