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	$18.82	11.166%	$20.9214	$20.92	$20.90	$20.90
Purchase #2	$83.55	8.266%	$90.4562	$90.46	$90.45	$90.50
Purchase #3	$105.57	3.160%	$108.906	$108.91	$108.90	$108.90
Purchase #4	$24.57	5.332%	$25.8801	$25.88	$25.90	$25.90
Purchase #5	$9.59	5.747%	$10.1411	$10.14	$10.15	$10.10
Purchase #6	$226.72	12.568%	$255.2142	$255.21	$255.20	$255.20
Purchase #7	$29.65	8.183%	$32.0763	$32.08	$32.10	$32.10
7 purchase totals =	$498.47		$543.5953	$543.60	$543.60	$543.60