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	$206.67	4.262%	$215.4783	$215.48	$215.50	$215.50
Purchase #2	$129.84	6.446%	$138.2095	$138.21	$138.20	$138.20
Purchase #3	$126.45	5.111%	$132.9129	$132.91	$132.90	$132.90
Purchase #4	$59.49	11.285%	$66.2034	$66.20	$66.20	$66.20
Purchase #5	$35.41	13.384%	$40.1493	$40.15	$40.15	$40.10
Purchase #6	$29.41	8.384%	$31.8757	$31.88	$31.90	$31.90
Purchase #7	$79.48	13.171%	$89.9483	$89.95	$89.95	$89.90
7 purchase totals =	$666.75		$714.7774	$714.78	$714.80	$714.70