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	$100.92	10.579%	$111.5963	$111.60	$111.60	$111.60
Purchase #2	$71.91	12.298%	$80.7535	$80.75	$80.75	$80.80
Purchase #3	$42.29	5.354%	$44.5542	$44.55	$44.55	$44.60
Purchase #4	$175.45	8.280%	$189.9773	$189.98	$190.00	$190.00
Purchase #5	$219.76	8.477%	$238.3891	$238.39	$238.40	$238.40
Purchase #6	$98.31	6.469%	$104.6697	$104.67	$104.65	$104.70
Purchase #7	$7.66	11.798%	$8.5637	$8.56	$8.55	$8.60
7 purchase totals =	$716.30		$778.5038	$778.50	$778.50	$778.70