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	$90.93	9.284%	$99.3719	$99.37	$99.35	$99.40
Purchase #2	$70.79	13.771%	$80.5385	$80.54	$80.55	$80.50
Purchase #3	$54.51	10.293%	$60.1207	$60.12	$60.10	$60.10
Purchase #4	$38.70	4.341%	$40.38	$40.38	$40.40	$40.40
Purchase #5	$39.48	8.479%	$42.8275	$42.83	$42.85	$42.80
Purchase #6	$194.46	6.798%	$207.6794	$207.68	$207.70	$207.70
Purchase #7	$160.69	13.636%	$182.6017	$182.60	$182.60	$182.60
7 purchase totals =	$649.56		$713.5197	$713.52	$713.55	$713.50