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	$159.72	13.820%	$181.7933	$181.79	$181.80	$181.80
Purchase #2	$223.86	6.714%	$238.89	$238.89	$238.90	$238.90
Purchase #3	$103.89	3.179%	$107.1927	$107.19	$107.20	$107.20
Purchase #4	$47.87	7.162%	$51.2984	$51.30	$51.30	$51.30
Purchase #5	$128.49	7.795%	$138.5058	$138.51	$138.50	$138.50
Purchase #6	$113.49	9.534%	$124.3101	$124.31	$124.30	$124.30
Purchase #7	$213.58	13.837%	$243.1331	$243.13	$243.15	$243.10
7 purchase totals =	$990.90		$1,085.1234	$1,085.12	$1,085.15	$1,085.10