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	$235.83	13.368%	$267.3558	$267.36	$267.35	$267.40
Purchase #2	$73.93	6.787%	$78.9476	$78.95	$78.95	$78.90
Purchase #3	$38.62	10.516%	$42.6813	$42.68	$42.70	$42.70
Purchase #4	$189.96	9.721%	$208.426	$208.43	$208.45	$208.40
Purchase #5	$246.45	3.288%	$254.5533	$254.55	$254.55	$254.60
Purchase #6	$20.31	7.362%	$21.8052	$21.81	$21.80	$21.80
Purchase #7	$132.95	9.203%	$145.1854	$145.19	$145.20	$145.20
7 purchase totals =	$938.05		$1,018.9546	$1,018.97	$1,019.00	$1,019.00