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	$177.56	4.797%	$186.0776	$186.08	$186.10	$186.10
Purchase #2	$132.82	5.294%	$139.8515	$139.85	$139.85	$139.90
Purchase #3	$110.39	8.349%	$119.6065	$119.61	$119.60	$119.60
Purchase #4	$228.34	13.594%	$259.3805	$259.38	$259.40	$259.40
Purchase #5	$46.91	8.839%	$51.0564	$51.06	$51.05	$51.10
Purchase #6	$37.27	13.245%	$42.2064	$42.21	$42.20	$42.20
Purchase #7	$59.69	10.409%	$65.9031	$65.90	$65.90	$65.90
7 purchase totals =	$792.98		$864.0820	$864.09	$864.10	$864.20