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	$29.41	7.122%	$31.5046	$31.50	$31.50	$31.50
Purchase #2	$12.26	10.770%	$13.5804	$13.58	$13.60	$13.60
Purchase #3	$35.56	7.284%	$38.1502	$38.15	$38.15	$38.20
Purchase #4	$39.51	6.504%	$42.0797	$42.08	$42.10	$42.10
Purchase #5	$111.38	10.627%	$123.2164	$123.22	$123.20	$123.20
Purchase #6	$146.86	6.846%	$156.914	$156.91	$156.90	$156.90
Purchase #7	$178.63	5.382%	$188.2439	$188.24	$188.25	$188.20
7 purchase totals =	$553.61		$593.6892	$593.68	$593.70	$593.70