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	$101.33	10.777%	$112.2503	$112.25	$112.25	$112.30
Purchase #2	$51.52	5.470%	$54.3381	$54.34	$54.35	$54.30
Purchase #3	$72.29	10.612%	$79.9614	$79.96	$79.95	$80.00
Purchase #4	$42.50	9.703%	$46.6238	$46.62	$46.60	$46.60
Purchase #5	$80.82	10.555%	$89.3506	$89.35	$89.35	$89.40
Purchase #6	$26.67	9.184%	$29.1194	$29.12	$29.10	$29.10
Purchase #7	$138.72	12.726%	$156.3735	$156.37	$156.35	$156.40
7 purchase totals =	$513.85		$568.0171	$568.01	$567.95	$568.10