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	$68.72	5.589%	$72.5608	$72.56	$72.55	$72.60
Purchase #2	$211.64	4.618%	$221.4135	$221.41	$221.40	$221.40
Purchase #3	$248.84	7.307%	$267.0227	$267.02	$267.00	$267.00
Purchase #4	$103.51	13.537%	$117.5221	$117.52	$117.50	$117.50
Purchase #5	$27.58	13.332%	$31.257	$31.26	$31.25	$31.30
Purchase #6	$24.99	8.540%	$27.1241	$27.12	$27.10	$27.10
Purchase #7	$104.64	6.617%	$111.564	$111.56	$111.55	$111.60
7 purchase totals =	$789.92		$848.4642	$848.45	$848.35	$848.50