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	$88.81	11.511%	$99.0329	$99.03	$99.05	$99.00
Purchase #2	$154.68	4.798%	$162.1015	$162.10	$162.10	$162.10
Purchase #3	$149.82	12.400%	$168.3977	$168.40	$168.40	$168.40
Purchase #4	$38.79	9.441%	$42.4522	$42.45	$42.45	$42.50
Purchase #5	$73.70	8.669%	$80.0891	$80.09	$80.10	$80.10
Purchase #6	$124.33	9.849%	$136.5753	$136.58	$136.60	$136.60
Purchase #7	$44.60	10.742%	$49.3909	$49.39	$49.40	$49.40
7 purchase totals =	$674.73		$738.0396	$738.04	$738.10	$738.10