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	$143.83	9.161%	$157.0063	$157.01	$157.00	$157.00
Purchase #2	$51.51	7.396%	$55.3197	$55.32	$55.30	$55.30
Purchase #3	$175.87	4.274%	$183.3867	$183.39	$183.40	$183.40
Purchase #4	$183.96	6.865%	$196.5889	$196.59	$196.60	$196.60
Purchase #5	$121.96	7.575%	$131.1985	$131.20	$131.20	$131.20
Purchase #6	$155.41	8.346%	$168.3805	$168.38	$168.40	$168.40
Purchase #7	$167.81	12.192%	$188.2694	$188.27	$188.25	$188.30
7 purchase totals =	$1,000.35		$1,080.1500	$1,080.16	$1,080.15	$1,080.20