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	$103.85	7.673%	$111.8184	$111.82	$111.80	$111.80
Purchase #2	$217.82	9.594%	$238.7177	$238.72	$238.70	$238.70
Purchase #3	$202.67	9.258%	$221.4332	$221.43	$221.45	$221.40
Purchase #4	$206.31	10.607%	$228.1933	$228.19	$228.20	$228.20
Purchase #5	$170.98	8.634%	$185.7424	$185.74	$185.75	$185.70
Purchase #6	$239.59	10.769%	$265.3914	$265.39	$265.40	$265.40
Purchase #7	$27.31	13.670%	$31.0433	$31.04	$31.05	$31.00
7 purchase totals =	$1,168.53		$1,282.3397	$1,282.33	$1,282.35	$1,282.20