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	$13.44	13.275%	$15.2242	$15.22	$15.20	$15.20
Purchase #2	$159.28	7.466%	$171.1718	$171.17	$171.15	$171.20
Purchase #3	$230.44	12.294%	$258.7703	$258.77	$258.75	$258.80
Purchase #4	$157.48	5.582%	$166.2705	$166.27	$166.25	$166.30
Purchase #5	$246.59	13.709%	$280.395	$280.40	$280.40	$280.40
Purchase #6	$127.86	4.473%	$133.5792	$133.58	$133.60	$133.60
Purchase #7	$82.58	10.651%	$91.3756	$91.38	$91.40	$91.40
7 purchase totals =	$1,017.67		$1,116.7866	$1,116.79	$1,116.75	$1,116.90