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	$164.94	12.316%	$185.254	$185.25	$185.25	$185.30
Purchase #2	$152.32	4.340%	$158.9307	$158.93	$158.95	$158.90
Purchase #3	$90.86	7.319%	$97.51	$97.51	$97.50	$97.50
Purchase #4	$54.55	5.564%	$57.5852	$57.59	$57.60	$57.60
Purchase #5	$98.58	6.538%	$105.0252	$105.03	$105.05	$105.00
Purchase #6	$120.35	6.866%	$128.6132	$128.61	$128.60	$128.60
Purchase #7	$245.53	8.772%	$267.0679	$267.07	$267.05	$267.10
7 purchase totals =	$927.13		$999.9862	$999.99	$1,000.00	$1,000.00