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	$95.85	9.809%	$105.2519	$105.25	$105.25	$105.30
Purchase #2	$164.74	9.264%	$180.0015	$180.00	$180.00	$180.00
Purchase #3	$123.60	12.306%	$138.8102	$138.81	$138.80	$138.80
Purchase #4	$228.78	7.582%	$246.1261	$246.13	$246.15	$246.10
Purchase #5	$104.29	11.735%	$116.5284	$116.53	$116.55	$116.50
Purchase #6	$166.34	13.300%	$188.4632	$188.46	$188.45	$188.50
Purchase #7	$30.85	7.841%	$33.2689	$33.27	$33.25	$33.30
7 purchase totals =	$914.45		$1,008.4502	$1,008.45	$1,008.45	$1,008.50