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	$231.72	10.577%	$256.229	$256.23	$256.25	$256.20
Purchase #2	$55.27	5.509%	$58.3148	$58.31	$58.30	$58.30
Purchase #3	$34.26	11.589%	$38.2304	$38.23	$38.25	$38.20
Purchase #4	$206.89	7.726%	$222.8743	$222.87	$222.85	$222.90
Purchase #5	$62.95	3.268%	$65.0072	$65.01	$65.00	$65.00
Purchase #6	$133.45	9.371%	$145.9556	$145.96	$145.95	$146.00
Purchase #7	$39.38	4.577%	$41.1824	$41.18	$41.20	$41.20
7 purchase totals =	$763.92		$827.7937	$827.79	$827.80	$827.80