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	$66.57	8.614%	$72.3043	$72.30	$72.30	$72.30
Purchase #2	$246.55	6.473%	$262.5092	$262.51	$262.50	$262.50
Purchase #3	$132.83	12.316%	$149.1893	$149.19	$149.20	$149.20
Purchase #4	$51.93	7.249%	$55.6944	$55.69	$55.70	$55.70
Purchase #5	$33.89	5.545%	$35.7692	$35.77	$35.75	$35.80
Purchase #6	$29.27	12.277%	$32.8635	$32.86	$32.85	$32.90
Purchase #7	$27.75	12.535%	$31.2285	$31.23	$31.25	$31.20
7 purchase totals =	$588.79		$639.5584	$639.55	$639.55	$639.60