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	$171.44	8.595%	$186.1753	$186.18	$186.20	$186.20
Purchase #2	$136.67	4.133%	$142.3186	$142.32	$142.30	$142.30
Purchase #3	$57.53	3.571%	$59.5844	$59.58	$59.60	$59.60
Purchase #4	$25.77	5.824%	$27.2708	$27.27	$27.25	$27.30
Purchase #5	$250.56	10.293%	$276.3501	$276.35	$276.35	$276.40
Purchase #6	$70.93	12.806%	$80.0133	$80.01	$80.00	$80.00
Purchase #7	$130.54	11.572%	$145.6461	$145.65	$145.65	$145.60
7 purchase totals =	$843.44		$917.3586	$917.36	$917.35	$917.40