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	$116.90	5.491%	$123.319	$123.32	$123.30	$123.30
Purchase #2	$137.71	9.832%	$151.2496	$151.25	$151.25	$151.20
Purchase #3	$198.84	5.408%	$209.5933	$209.59	$209.60	$209.60
Purchase #4	$54.74	13.698%	$62.2383	$62.24	$62.25	$62.20
Purchase #5	$88.85	10.624%	$98.2894	$98.29	$98.30	$98.30
Purchase #6	$125.85	9.356%	$137.6245	$137.62	$137.60	$137.60
Purchase #7	$36.59	6.487%	$38.9636	$38.96	$38.95	$39.00
7 purchase totals =	$759.48		$821.2777	$821.27	$821.25	$821.20