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	$164.87	9.763%	$180.9663	$180.97	$180.95	$181.00
Purchase #2	$104.72	7.853%	$112.9437	$112.94	$112.95	$112.90
Purchase #3	$185.46	11.823%	$207.3869	$207.39	$207.40	$207.40
Purchase #4	$45.58	4.441%	$47.6042	$47.60	$47.60	$47.60
Purchase #5	$146.72	10.584%	$162.2488	$162.25	$162.25	$162.20
Purchase #6	$69.85	3.483%	$72.2829	$72.28	$72.30	$72.30
Purchase #7	$83.55	3.442%	$86.4258	$86.43	$86.45	$86.40
7 purchase totals =	$800.75		$869.8586	$869.86	$869.90	$869.80