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	$150.34	8.390%	$162.9535	$162.95	$162.95	$163.00
Purchase #2	$6.32	8.221%	$6.8396	$6.84	$6.85	$6.80
Purchase #3	$116.45	5.864%	$123.2786	$123.28	$123.30	$123.30
Purchase #4	$159.84	3.125%	$164.835	$164.84	$164.85	$164.80
Purchase #5	$16.94	7.871%	$18.2733	$18.27	$18.25	$18.30
Purchase #6	$147.28	4.289%	$153.5968	$153.60	$153.60	$153.60
Purchase #7	$35.37	5.670%	$37.3755	$37.38	$37.40	$37.40
7 purchase totals =	$632.54		$667.1523	$667.16	$667.20	$667.20