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	$120.86	6.487%	$128.7002	$128.70	$128.70	$128.70
Purchase #2	$177.88	12.213%	$199.6045	$199.60	$199.60	$199.60
Purchase #3	$191.71	3.524%	$198.4659	$198.47	$198.45	$198.50
Purchase #4	$101.52	9.552%	$111.2172	$111.22	$111.20	$111.20
Purchase #5	$245.37	11.550%	$273.7102	$273.71	$273.70	$273.70
Purchase #6	$90.69	10.161%	$99.905	$99.91	$99.90	$99.90
Purchase #7	$107.84	10.718%	$119.3983	$119.40	$119.40	$119.40
7 purchase totals =	$1,035.87		$1,131.0013	$1,131.01	$1,130.95	$1,131.00