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	$79.52	7.189%	$85.2367	$85.24	$85.25	$85.20
Purchase #2	$74.78	3.454%	$77.3629	$77.36	$77.35	$77.40
Purchase #3	$111.61	11.537%	$124.4864	$124.49	$124.50	$124.50
Purchase #4	$65.52	5.459%	$69.0967	$69.10	$69.10	$69.10
Purchase #5	$132.73	4.377%	$138.5396	$138.54	$138.55	$138.50
Purchase #6	$99.88	12.638%	$112.5028	$112.50	$112.50	$112.50
Purchase #7	$45.60	12.577%	$51.3351	$51.34	$51.35	$51.30
7 purchase totals =	$609.64		$658.5602	$658.57	$658.60	$658.50