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	$146.54	12.254%	$164.497	$164.50	$164.50	$164.50
Purchase #2	$108.79	11.629%	$121.4412	$121.44	$121.45	$121.40
Purchase #3	$152.95	8.842%	$166.4738	$166.47	$166.45	$166.50
Purchase #4	$47.42	6.150%	$50.3363	$50.34	$50.35	$50.30
Purchase #5	$73.71	10.558%	$81.4923	$81.49	$81.50	$81.50
Purchase #6	$59.95	13.136%	$67.825	$67.83	$67.85	$67.80
Purchase #7	$138.35	3.252%	$142.8491	$142.85	$142.85	$142.80
7 purchase totals =	$727.71		$794.9147	$794.92	$794.95	$794.80