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	$228.34	9.214%	$249.3792	$249.38	$249.40	$249.40
Purchase #2	$82.93	3.122%	$85.5191	$85.52	$85.50	$85.50
Purchase #3	$184.89	5.671%	$195.3751	$195.38	$195.40	$195.40
Purchase #4	$111.99	8.183%	$121.1541	$121.15	$121.15	$121.20
Purchase #5	$40.70	6.647%	$43.4053	$43.41	$43.40	$43.40
Purchase #6	$158.59	13.667%	$180.2645	$180.26	$180.25	$180.30
Purchase #7	$230.83	7.549%	$248.2554	$248.26	$248.25	$248.30
7 purchase totals =	$1,038.27		$1,123.3527	$1,123.36	$1,123.35	$1,123.50