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	$165.81	13.385%	$188.0037	$188.00	$188.00	$188.00
Purchase #2	$173.50	4.189%	$180.7679	$180.77	$180.75	$180.80
Purchase #3	$183.92	8.687%	$199.8971	$199.90	$199.90	$199.90
Purchase #4	$97.92	11.575%	$109.2542	$109.25	$109.25	$109.30
Purchase #5	$155.59	3.838%	$161.5615	$161.56	$161.55	$161.60
Purchase #6	$45.73	13.487%	$51.8976	$51.90	$51.90	$51.90
Purchase #7	$167.90	11.130%	$186.5873	$186.59	$186.60	$186.60
7 purchase totals =	$990.37		$1,077.9693	$1,077.97	$1,077.95	$1,078.10