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	$226.96	13.399%	$257.3704	$257.37	$257.35	$257.40
Purchase #2	$35.83	7.729%	$38.5993	$38.60	$38.60	$38.60
Purchase #3	$56.81	5.528%	$59.9505	$59.95	$59.95	$60.00
Purchase #4	$34.29	3.797%	$35.592	$35.59	$35.60	$35.60
Purchase #5	$106.52	12.524%	$119.8606	$119.86	$119.85	$119.90
Purchase #6	$213.84	13.853%	$243.4633	$243.46	$243.45	$243.50
Purchase #7	$49.37	11.149%	$54.8743	$54.87	$54.85	$54.90
7 purchase totals =	$723.62		$809.7104	$809.70	$809.65	$809.90