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	$50.62	12.160%	$56.7754	$56.78	$56.80	$56.80
Purchase #2	$143.90	4.481%	$150.3482	$150.35	$150.35	$150.30
Purchase #3	$170.47	8.570%	$185.0793	$185.08	$185.10	$185.10
Purchase #4	$163.37	6.842%	$174.5478	$174.55	$174.55	$174.50
Purchase #5	$14.64	7.782%	$15.7793	$15.78	$15.80	$15.80
Purchase #6	$169.43	9.649%	$185.7783	$185.78	$185.80	$185.80
Purchase #7	$95.45	10.505%	$105.477	$105.48	$105.50	$105.50
7 purchase totals =	$807.88		$873.7853	$873.80	$873.90	$873.80