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	$17.75	3.480%	$18.3677	$18.37	$18.35	$18.40
Purchase #2	$25.67	13.604%	$29.1621	$29.16	$29.15	$29.20
Purchase #3	$101.99	7.106%	$109.2374	$109.24	$109.25	$109.20
Purchase #4	$227.77	12.337%	$255.87	$255.87	$255.85	$255.90
Purchase #5	$139.76	4.652%	$146.2616	$146.26	$146.25	$146.30
Purchase #6	$217.92	4.837%	$228.4608	$228.46	$228.45	$228.50
Purchase #7	$70.54	3.392%	$72.9327	$72.93	$72.95	$72.90
7 purchase totals =	$801.40		$860.2923	$860.29	$860.25	$860.40