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	$79.87	6.536%	$85.0903	$85.09	$85.10	$85.10
Purchase #2	$39.36	8.161%	$42.5722	$42.57	$42.55	$42.60
Purchase #3	$130.29	12.729%	$146.8746	$146.87	$146.85	$146.90
Purchase #4	$144.55	4.852%	$151.5636	$151.56	$151.55	$151.60
Purchase #5	$116.37	12.713%	$131.1641	$131.16	$131.15	$131.20
Purchase #6	$126.44	4.829%	$132.5458	$132.55	$132.55	$132.50
Purchase #7	$106.50	9.247%	$116.3481	$116.35	$116.35	$116.30
7 purchase totals =	$743.38		$806.1587	$806.15	$806.10	$806.20