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	$9.69	9.299%	$10.5911	$10.59	$10.60	$10.60
Purchase #2	$104.84	13.277%	$118.7596	$118.76	$118.75	$118.80
Purchase #3	$106.26	3.384%	$109.8558	$109.86	$109.85	$109.90
Purchase #4	$193.85	13.462%	$219.9461	$219.95	$219.95	$219.90
Purchase #5	$121.58	5.727%	$128.5429	$128.54	$128.55	$128.50
Purchase #6	$152.59	6.510%	$162.5236	$162.52	$162.50	$162.50
Purchase #7	$6.62	9.645%	$7.2585	$7.26	$7.25	$7.30
7 purchase totals =	$695.43		$757.4776	$757.48	$757.45	$757.50