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	$160.31	8.223%	$173.4923	$173.49	$173.50	$173.50
Purchase #2	$40.86	13.567%	$46.4035	$46.40	$46.40	$46.40
Purchase #3	$82.70	6.797%	$88.3211	$88.32	$88.30	$88.30
Purchase #4	$41.53	3.691%	$43.0629	$43.06	$43.05	$43.10
Purchase #5	$101.57	8.311%	$110.0115	$110.01	$110.00	$110.00
Purchase #6	$86.80	4.147%	$90.3996	$90.40	$90.40	$90.40
Purchase #7	$109.67	12.488%	$123.3656	$123.37	$123.35	$123.40
7 purchase totals =	$623.44		$675.0565	$675.05	$675.00	$675.10