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	$79.78	3.671%	$82.7087	$82.71	$82.70	$82.70
Purchase #2	$142.97	13.382%	$162.1022	$162.10	$162.10	$162.10
Purchase #3	$149.72	4.362%	$156.2508	$156.25	$156.25	$156.30
Purchase #4	$103.71	5.357%	$109.2657	$109.27	$109.25	$109.30
Purchase #5	$15.80	7.747%	$17.024	$17.02	$17.00	$17.00
Purchase #6	$100.69	8.615%	$109.3644	$109.36	$109.35	$109.40
Purchase #7	$182.69	4.374%	$190.6809	$190.68	$190.70	$190.70
7 purchase totals =	$775.36		$827.3967	$827.39	$827.35	$827.50