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	$100.83	6.461%	$107.3446	$107.34	$107.35	$107.30
Purchase #2	$145.73	8.803%	$158.5586	$158.56	$158.55	$158.60
Purchase #3	$185.92	12.346%	$208.8737	$208.87	$208.85	$208.90
Purchase #4	$88.94	4.855%	$93.258	$93.26	$93.25	$93.30
Purchase #5	$174.58	9.740%	$191.5841	$191.58	$191.60	$191.60
Purchase #6	$117.94	11.591%	$131.6104	$131.61	$131.60	$131.60
Purchase #7	$98.43	10.103%	$108.3744	$108.37	$108.35	$108.40
7 purchase totals =	$912.37		$999.6038	$999.59	$999.55	$999.70