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	$89.74	11.724%	$100.2611	$100.26	$100.25	$100.30
Purchase #2	$122.95	4.587%	$128.5897	$128.59	$128.60	$128.60
Purchase #3	$11.84	9.264%	$12.9369	$12.94	$12.95	$12.90
Purchase #4	$30.25	9.726%	$33.1921	$33.19	$33.20	$33.20
Purchase #5	$221.31	10.743%	$245.0853	$245.09	$245.10	$245.10
Purchase #6	$219.89	7.417%	$236.1992	$236.20	$236.20	$236.20
Purchase #7	$38.61	13.758%	$43.922	$43.92	$43.90	$43.90
7 purchase totals =	$734.59		$800.1863	$800.19	$800.20	$800.20