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	$94.32	9.778%	$103.5426	$103.54	$103.55	$103.50
Purchase #2	$56.67	10.473%	$62.605	$62.61	$62.60	$62.60
Purchase #3	$131.69	8.314%	$142.6387	$142.64	$142.65	$142.60
Purchase #4	$50.59	13.421%	$57.3797	$57.38	$57.40	$57.40
Purchase #5	$90.71	10.146%	$99.9134	$99.91	$99.90	$99.90
Purchase #6	$74.82	8.689%	$81.3211	$81.32	$81.30	$81.30
Purchase #7	$12.87	10.210%	$14.184	$14.18	$14.20	$14.20
7 purchase totals =	$511.67		$561.5845	$561.58	$561.60	$561.50