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	$51.81	10.112%	$57.049	$57.05	$57.05	$57.00
Purchase #2	$119.61	9.667%	$131.1727	$131.17	$131.15	$131.20
Purchase #3	$40.31	7.362%	$43.2776	$43.28	$43.30	$43.30
Purchase #4	$25.90	7.567%	$27.8599	$27.86	$27.85	$27.90
Purchase #5	$111.35	10.590%	$123.142	$123.14	$123.15	$123.10
Purchase #6	$162.85	9.407%	$178.1693	$178.17	$178.15	$178.20
Purchase #7	$43.54	11.135%	$48.3882	$48.39	$48.40	$48.40
7 purchase totals =	$555.37		$609.0587	$609.06	$609.05	$609.10