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	$54.59	13.620%	$62.0252	$62.03	$62.05	$62.00
Purchase #2	$63.33	9.132%	$69.1133	$69.11	$69.10	$69.10
Purchase #3	$18.39	10.200%	$20.2658	$20.27	$20.25	$20.30
Purchase #4	$229.97	11.256%	$255.8554	$255.86	$255.85	$255.90
Purchase #5	$9.78	7.149%	$10.4792	$10.48	$10.50	$10.50
Purchase #6	$219.61	3.326%	$226.9142	$226.91	$226.90	$226.90
Purchase #7	$14.97	6.138%	$15.8889	$15.89	$15.90	$15.90
7 purchase totals =	$610.64		$660.5420	$660.55	$660.55	$660.60