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	$91.48	13.136%	$103.4968	$103.50	$103.50	$103.50
Purchase #2	$183.99	4.647%	$192.54	$192.54	$192.55	$192.50
Purchase #3	$90.59	4.430%	$94.6031	$94.60	$94.60	$94.60
Purchase #4	$70.74	11.493%	$78.8701	$78.87	$78.85	$78.90
Purchase #5	$98.97	3.393%	$102.3281	$102.33	$102.35	$102.30
Purchase #6	$53.31	11.514%	$59.4481	$59.45	$59.45	$59.40
Purchase #7	$153.63	9.332%	$167.9668	$167.97	$167.95	$168.00
7 purchase totals =	$742.71		$799.2530	$799.26	$799.25	$799.20