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	$237.74	12.154%	$266.6349	$266.63	$266.65	$266.60
Purchase #2	$233.92	4.673%	$244.8511	$244.85	$244.85	$244.90
Purchase #3	$37.42	9.320%	$40.9075	$40.91	$40.90	$40.90
Purchase #4	$178.97	7.158%	$191.7807	$191.78	$191.80	$191.80
Purchase #5	$177.29	4.547%	$185.3514	$185.35	$185.35	$185.40
Purchase #6	$198.33	11.633%	$221.4017	$221.40	$221.40	$221.40
Purchase #7	$101.35	10.185%	$111.6725	$111.67	$111.65	$111.70
7 purchase totals =	$1,165.02		$1,262.5998	$1,262.59	$1,262.60	$1,262.70