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	$83.80	7.816%	$90.3498	$90.35	$90.35	$90.30
Purchase #2	$157.54	3.333%	$162.7908	$162.79	$162.80	$162.80
Purchase #3	$236.82	12.509%	$266.4438	$266.44	$266.45	$266.40
Purchase #4	$12.94	5.321%	$13.6285	$13.63	$13.65	$13.60
Purchase #5	$226.53	8.330%	$245.3999	$245.40	$245.40	$245.40
Purchase #6	$119.26	6.572%	$127.0978	$127.10	$127.10	$127.10
Purchase #7	$133.98	13.391%	$151.9213	$151.92	$151.90	$151.90
7 purchase totals =	$970.87		$1,057.6319	$1,057.63	$1,057.65	$1,057.50