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	$24.74	8.870%	$26.9344	$26.93	$26.95	$26.90
Purchase #2	$228.40	5.231%	$240.3476	$240.35	$240.35	$240.30
Purchase #3	$121.30	4.767%	$127.0824	$127.08	$127.10	$127.10
Purchase #4	$248.83	5.685%	$262.976	$262.98	$263.00	$263.00
Purchase #5	$75.93	5.785%	$80.3226	$80.32	$80.30	$80.30
Purchase #6	$41.78	9.243%	$45.6417	$45.64	$45.65	$45.60
Purchase #7	$39.52	8.531%	$42.8915	$42.89	$42.90	$42.90
7 purchase totals =	$780.50		$826.1962	$826.19	$826.25	$826.10