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	$113.31	13.360%	$128.4482	$128.45	$128.45	$128.40
Purchase #2	$54.72	5.664%	$57.8193	$57.82	$57.80	$57.80
Purchase #3	$72.45	11.509%	$80.7883	$80.79	$80.80	$80.80
Purchase #4	$170.32	5.723%	$180.0674	$180.07	$180.05	$180.10
Purchase #5	$202.65	11.144%	$225.2333	$225.23	$225.25	$225.20
Purchase #6	$222.27	9.104%	$242.5055	$242.51	$242.50	$242.50
Purchase #7	$142.52	7.324%	$152.9582	$152.96	$152.95	$153.00
7 purchase totals =	$978.24		$1,067.8202	$1,067.83	$1,067.80	$1,067.80