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	$139.65	3.237%	$144.1705	$144.17	$144.15	$144.20
Purchase #2	$115.79	10.580%	$128.0406	$128.04	$128.05	$128.00
Purchase #3	$98.60	4.700%	$103.2342	$103.23	$103.25	$103.20
Purchase #4	$162.82	7.537%	$175.0917	$175.09	$175.10	$175.10
Purchase #5	$78.68	5.509%	$83.0145	$83.01	$83.00	$83.00
Purchase #6	$41.25	11.475%	$45.9834	$45.98	$46.00	$46.00
Purchase #7	$104.99	10.599%	$116.1179	$116.12	$116.10	$116.10
7 purchase totals =	$741.78		$795.6528	$795.64	$795.65	$795.60