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	$74.96	10.581%	$82.8915	$82.89	$82.90	$82.90
Purchase #2	$132.59	7.549%	$142.5992	$142.60	$142.60	$142.60
Purchase #3	$186.48	11.744%	$208.3802	$208.38	$208.40	$208.40
Purchase #4	$105.68	10.109%	$116.3632	$116.36	$116.35	$116.40
Purchase #5	$170.97	8.386%	$185.3075	$185.31	$185.30	$185.30
Purchase #6	$97.92	12.131%	$109.7987	$109.80	$109.80	$109.80
Purchase #7	$49.27	8.515%	$53.4653	$53.47	$53.45	$53.50
7 purchase totals =	$817.87		$898.8056	$898.81	$898.80	$898.90