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	$38.99	11.507%	$43.4766	$43.48	$43.50	$43.50
Purchase #2	$14.33	7.276%	$15.3727	$15.37	$15.35	$15.40
Purchase #3	$9.95	13.823%	$11.3254	$11.33	$11.35	$11.30
Purchase #4	$96.25	13.842%	$109.5729	$109.57	$109.55	$109.60
Purchase #5	$176.45	11.627%	$196.9658	$196.97	$196.95	$197.00
Purchase #6	$81.76	6.208%	$86.8357	$86.84	$86.85	$86.80
Purchase #7	$85.49	7.126%	$91.582	$91.58	$91.60	$91.60
7 purchase totals =	$503.22		$555.1311	$555.14	$555.15	$555.20